diff --git a/jooby/pom.xml b/jooby/pom.xml
index dcf1a87d91..70d047aa29 100644
--- a/jooby/pom.xml
+++ b/jooby/pom.xml
@@ -94,6 +94,12 @@
   </build>
 
   <dependencies>
+    <dependency>
+      <groupId>com.google.code.findbugs</groupId>
+      <artifactId>jsr305</artifactId>
+      <scope>provided</scope>
+    </dependency>
+
     <!-- Logging System -->
     <dependency>
       <groupId>org.slf4j</groupId>
diff --git a/jooby/src/main/java/org/jooby/Asset.java b/jooby/src/main/java/org/jooby/Asset.java
index df226e8162..9f8a9a2827 100644
--- a/jooby/src/main/java/org/jooby/Asset.java
+++ b/jooby/src/main/java/org/jooby/Asset.java
@@ -211,6 +211,8 @@
 import com.google.common.io.BaseEncoding;
 import com.google.common.primitives.Longs;
 
+import javax.annotation.Nonnull;
+
 /**
  * Usually a public file/resource like javascript, css, images files, etc...
  * An asset consist of content type, stream and last modified since attributes, between others.
@@ -286,6 +288,7 @@ public MediaType type() {
    *
    * @return The asset name (without path).
    */
+  @Nonnull
   default String name() {
     String path = path();
     int slash = path.lastIndexOf('/');
@@ -302,17 +305,20 @@ default String name() {
    *
    * @return The asset requested path, includes the name.
    */
+  @Nonnull
   String path();
 
   /**
    * @return URL representing the resource.
    */
+  @Nonnull
   URL resource();
 
   /**
    * @return Generate a weak Etag using the {@link #path()}, {@link #lastModified()} and
    *         {@link #length()}.
    */
+  @Nonnull
   default String etag() {
     StringBuilder b = new StringBuilder(32);
     b.append("W/\"");
@@ -340,10 +346,12 @@ default String etag() {
    * @return The content of this asset.
    * @throws Exception If content can't be read it.
    */
+  @Nonnull
   InputStream stream() throws Exception;
 
   /**
    * @return Asset media type.
    */
+  @Nonnull
   MediaType type();
 }
diff --git a/jooby/src/main/java/org/jooby/Cookie.java b/jooby/src/main/java/org/jooby/Cookie.java
index fcb11011ed..870313aa05 100644
--- a/jooby/src/main/java/org/jooby/Cookie.java
+++ b/jooby/src/main/java/org/jooby/Cookie.java
@@ -210,6 +210,8 @@
 import org.jooby.funzy.Throwing;
 import org.jooby.internal.CookieImpl;
 
+import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
 import javax.crypto.Mac;
 import javax.crypto.spec.SecretKeySpec;
 import java.net.URLDecoder;
@@ -387,6 +389,7 @@ public Definition(final String name) {
      *
      * @return A new cookie.
      */
+    @Nonnull
     public Cookie toCookie() {
       return new CookieImpl(this);
     }
@@ -402,6 +405,7 @@ public String toString() {
      * @param name A cookie's name.
      * @return This definition.
      */
+    @Nonnull
     public Definition name(final String name) {
       this.name = requireNonNull(name, "A cookie name is required.");
       return this;
@@ -410,6 +414,7 @@ public Definition name(final String name) {
     /**
      * @return Cookie's name.
      */
+    @Nonnull
     public Optional<String> name() {
       return Optional.ofNullable(name);
     }
@@ -420,6 +425,7 @@ public Optional<String> name() {
      * @param value A value.
      * @return This definition.
      */
+    @Nonnull
     public Definition value(final String value) {
       this.value = requireNonNull(value, "A cookie value is required.");
       return this;
@@ -428,6 +434,7 @@ public Definition value(final String value) {
     /**
      * @return Cookie's value.
      */
+    @Nonnull
     public Optional<String> value() {
       if (Strings.isNullOrEmpty(value)) {
         return Optional.empty();
@@ -441,6 +448,7 @@ public Optional<String> value() {
      * @param domain Cookie's domain.
      * @return This definition.
      */
+    @Nonnull
     public Definition domain(final String domain) {
       this.domain = requireNonNull(domain, "A cookie domain is required.");
       return this;
@@ -449,6 +457,7 @@ public Definition domain(final String domain) {
     /**
      * @return A cookie's domain.
      */
+    @Nonnull
     public Optional<String> domain() {
       return Optional.ofNullable(domain);
     }
@@ -459,6 +468,7 @@ public Optional<String> domain() {
      * @param path Cookie's path.
      * @return This definition.
      */
+    @Nonnull
     public Definition path(final String path) {
       this.path = requireNonNull(path, "A cookie path is required.");
       return this;
@@ -467,6 +477,7 @@ public Definition path(final String path) {
     /**
      * @return Get cookie's path.
      */
+    @Nonnull
     public Optional<String> path() {
       return Optional.ofNullable(path);
     }
@@ -477,6 +488,7 @@ public Optional<String> path() {
      * @param comment A cookie's comment.
      * @return This definition.
      */
+    @Nonnull
     public Definition comment(final String comment) {
       this.comment = requireNonNull(comment, "A cookie comment is required.");
       return this;
@@ -485,6 +497,7 @@ public Definition comment(final String comment) {
     /**
      * @return Cookie's comment.
      */
+    @Nonnull
     public Optional<String> comment() {
       return Optional.ofNullable(comment);
     }
@@ -495,6 +508,7 @@ public Optional<String> comment() {
      * @param httpOnly True, for HTTP Only.
      * @return This definition.
      */
+    @Nonnull
     public Definition httpOnly(final boolean httpOnly) {
       this.httpOnly = httpOnly;
       return this;
@@ -503,6 +517,7 @@ public Definition httpOnly(final boolean httpOnly) {
     /**
      * @return HTTP only flag.
      */
+    @Nonnull
     public Optional<Boolean> httpOnly() {
       return Optional.ofNullable(httpOnly);
     }
@@ -513,6 +528,7 @@ public Optional<Boolean> httpOnly() {
      * @param secure True, ensure that the session cookie is only transmitted via HTTPS.
      * @return This definition.
      */
+    @Nonnull
     public Definition secure(final boolean secure) {
       this.secure = secure;
       return this;
@@ -521,6 +537,7 @@ public Definition secure(final boolean secure) {
     /**
      * @return True, ensure that the session cookie is only transmitted via HTTPS.
      */
+    @Nonnull
     public Optional<Boolean> secure() {
       return Optional.ofNullable(secure);
     }
@@ -543,6 +560,7 @@ public Optional<Boolean> secure() {
      * means the cookie is not stored; if zero, deletes the cookie.
      * @return This definition.
      */
+    @Nonnull
     public Definition maxAge(final int maxAge) {
       this.maxAge = maxAge;
       return this;
@@ -564,6 +582,7 @@ public Definition maxAge(final int maxAge) {
      *
      * @return Cookie's max age in seconds.
      */
+    @Nonnull
     public Optional<Integer> maxAge() {
       return Optional.ofNullable(maxAge);
     }
@@ -608,6 +627,7 @@ public class Signature {
      * @param secret A secret key.
      * @return A signed value.
      */
+    @Nonnull
     public static String sign(final String value, final String secret) {
       requireNonNull(value, "A value is required.");
       requireNonNull(secret, "A secret is required.");
@@ -628,8 +648,9 @@ public static String sign(final String value, final String secret) {
      *
      * @param value A signed value.
      * @param secret A secret key.
-     * @return A new signed value.
+     * @return A new signed value or null.
      */
+    @Nullable
     public static String unsign(final String value, final String secret) {
       requireNonNull(value, "A value is required.");
       requireNonNull(secret, "A secret is required.");
@@ -659,21 +680,25 @@ public static boolean valid(final String value, final String secret) {
   /**
    * @return Cookie's name.
    */
+  @Nonnull
   String name();
 
   /**
    * @return Cookie's value.
    */
+  @Nonnull
   Optional<String> value();
 
   /**
    * @return An optional comment.
    */
+  @Nonnull
   Optional<String> comment();
 
   /**
    * @return Cookie's domain.
    */
+  @Nonnull
   Optional<String> domain();
 
   /**
@@ -692,6 +717,7 @@ public static boolean valid(final String value, final String secret) {
   /**
    * @return Cookie's path.
    */
+  @Nonnull
   Optional<String> path();
 
   /**
@@ -710,5 +736,6 @@ public static boolean valid(final String value, final String secret) {
   /**
    * @return Encode the cookie.
    */
+  @Nonnull
   String encode();
 }
diff --git a/jooby/src/main/java/org/jooby/Deferred.java b/jooby/src/main/java/org/jooby/Deferred.java
index d9887c9d64..0d625ad695 100644
--- a/jooby/src/main/java/org/jooby/Deferred.java
+++ b/jooby/src/main/java/org/jooby/Deferred.java
@@ -205,6 +205,7 @@
 
 import static java.util.Objects.requireNonNull;
 
+import javax.annotation.Nonnull;
 import java.util.Optional;
 import java.util.concurrent.Callable;
 import java.util.concurrent.Executor;
@@ -331,7 +332,7 @@ public class Deferred extends Result {
    * @author edgar
    * @since 0.10.0
    */
-  public static interface Initializer0 {
+  public interface Initializer0 {
 
     /**
      * Run the initializer block.
@@ -348,7 +349,7 @@ public static interface Initializer0 {
    * @author edgar
    * @since 0.10.0
    */
-  public static interface Initializer {
+  public interface Initializer {
 
     /**
      * Run the initializer block.
@@ -366,7 +367,7 @@ public static interface Initializer {
    * @author edgar
    * @since 0.10.0
    */
-  public static interface Handler {
+  public interface Handler {
     void handle(Result result, Throwable exception);
   }
 
@@ -432,6 +433,7 @@ public Deferred() {
    * @param value Resolved value.
    */
   @Override
+  @Nonnull
   public Result set(final Object value) {
     if (value instanceof Throwable) {
       reject((Throwable) value);
@@ -447,6 +449,7 @@ public Result set(final Object value) {
    *
    * @return Executor to use or fallback to global/application executor.
    */
+  @Nonnull
   public Optional<String> executor() {
     return Optional.ofNullable(executor);
   }
@@ -456,6 +459,7 @@ public Optional<String> executor() {
    *
    * @return Name of the caller thread (thread that creates this deferred object).
    */
+  @Nonnull
   public String callerThread() {
     return callerThread;
   }
@@ -466,6 +470,7 @@ public String callerThread() {
    *
    * @param value A value for this deferred.
    */
+  @Nonnull
   public void resolve(final Object value) {
     if (value == null) {
       handler.handle(null, null);
@@ -539,6 +544,7 @@ public void handler(final Request req, final Handler handler) throws Exception {
    * @param handler Application block.
    * @return A new deferred handler.
    */
+  @Nonnull
   public static Deferred deferred(final Route.OneArgHandler handler) {
     return deferred(null, handler);
   }
@@ -574,6 +580,7 @@ public static Deferred deferred(final Route.OneArgHandler handler) {
    * @param handler Application block.
    * @return A new deferred.
    */
+  @Nonnull
   public static Deferred deferred(final Route.ZeroArgHandler handler) {
     return deferred(null, handler);
   }
@@ -599,6 +606,7 @@ public static Deferred deferred(final Route.ZeroArgHandler handler) {
    * @param handler Application block.
    * @return A new deferred handler.
    */
+  @Nonnull
   public static Deferred deferred(final String executor, final Route.ZeroArgHandler handler) {
     return deferred(executor, req -> handler.handle());
   }
@@ -624,6 +632,7 @@ public static Deferred deferred(final String executor, final Route.ZeroArgHandle
    * @param handler Application block.
    * @return A new deferred handler.
    */
+  @Nonnull
   public static Deferred deferred(final String executor, final Route.OneArgHandler handler) {
     return new Deferred(executor, (req, deferred) -> {
       try {
diff --git a/jooby/src/main/java/org/jooby/Env.java b/jooby/src/main/java/org/jooby/Env.java
index 906e882141..c406804263 100644
--- a/jooby/src/main/java/org/jooby/Env.java
+++ b/jooby/src/main/java/org/jooby/Env.java
@@ -211,6 +211,7 @@
 import static java.util.Objects.requireNonNull;
 import org.jooby.funzy.Throwing;
 
+import javax.annotation.Nonnull;
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.HashMap;
@@ -263,6 +264,7 @@ interface PropertySource {
      * @return Value or throw {@link NoSuchElementException}.
      * @throws NoSuchElementException If property is missing.
      */
+    @Nonnull
     String get(String key) throws NoSuchElementException;
   }
 
@@ -620,6 +622,7 @@ public Env xss(final String name, final Function<String, String> escaper) {
   /**
    * @return Env's name.
    */
+  @Nonnull
   String name();
 
   /**
@@ -628,21 +631,25 @@ public Env xss(final String name, final Function<String, String> escaper) {
    * @return Available {@link Router}.
    * @throws UnsupportedOperationException if router isn't available.
    */
+  @Nonnull
   Router router() throws UnsupportedOperationException;
 
   /**
    * @return environment properties.
    */
+  @Nonnull
   Config config();
 
   /**
    * @return Default locale from <code>application.lang</code>.
    */
+  @Nonnull
   Locale locale();
 
   /**
    * @return Utility method for generating keys for named services.
    */
+  @Nonnull
   default ServiceKey serviceKey() {
     return new ServiceKey();
   }
@@ -657,6 +664,7 @@ default ServiceKey serviceKey() {
    * @param text Text to process.
    * @return A processed string.
    */
+  @Nonnull
   default String resolve(final String text) {
     return resolver().resolve(text);
   }
@@ -666,6 +674,7 @@ default String resolve(final String text) {
    *
    * @return A resolver object.
    */
+  @Nonnull
   default Resolver resolver() {
     return new Resolver().source(config());
   }
@@ -678,6 +687,7 @@ default Resolver resolver() {
    * @param <T> A resulting type.
    * @return A resulting object.
    */
+  @Nonnull
   default <T> Optional<T> ifMode(final String name, final Supplier<T> fn) {
     if (name().equals(name)) {
       return Optional.of(fn.get());
@@ -688,6 +698,7 @@ default <T> Optional<T> ifMode(final String name, final Supplier<T> fn) {
   /**
    * @return XSS escape functions.
    */
+  @Nonnull
   Map<String, Function<String, String>> xss();
 
   /**
@@ -696,6 +707,7 @@ default <T> Optional<T> ifMode(final String name, final Supplier<T> fn) {
    * @param xss XSS to combine.
    * @return Chain of required xss functions.
    */
+  @Nonnull
   default Function<String, String> xss(final String... xss) {
     Map<String, Function<String, String>> fn = xss();
     BinaryOperator<Function<String, String>> reduce = Function::andThen;
@@ -713,21 +725,25 @@ default Function<String, String> xss(final String... xss) {
    * @param escaper Escape function.
    * @return This environment.
    */
+  @Nonnull
   Env xss(String name, Function<String, String> escaper);
 
   /**
    * @return List of start tasks.
    */
+  @Nonnull
   List<Throwing.Consumer<Registry>> startTasks();
 
   /**
    * @return List of start tasks.
    */
+  @Nonnull
   List<Throwing.Consumer<Registry>> startedTasks();
 
   /**
    * @return List of stop tasks.
    */
+  @Nonnull
   List<Throwing.Consumer<Registry>> stopTasks();
 
   /**
@@ -738,6 +754,7 @@ default Function<String, String> xss(final String... xss) {
    * @param <T> Object type.
    * @return This environment.
    */
+  @Nonnull
   <T> Env set(Key<T> key, T value);
 
   /**
@@ -748,6 +765,7 @@ default Function<String, String> xss(final String... xss) {
    * @param <T> Object type.
    * @return This environment.
    */
+  @Nonnull
   default <T> Env set(Class<T> key, T value) {
     return set(Key.get(key), value);
   }
@@ -759,6 +777,7 @@ default <T> Env set(Class<T> key, T value) {
    * @param <T> Object type.
    * @return Object valur or empty.
    */
+  @Nonnull
   <T> Optional<T> get(Key<T> key);
 
   /**
@@ -768,6 +787,7 @@ default <T> Env set(Class<T> key, T value) {
    * @param <T> Object type.
    * @return Object valur or empty.
    */
+  @Nonnull
   default <T> Optional<T> get(Class<T> key) {
     return get(Key.get(key));
   }
diff --git a/jooby/src/main/java/org/jooby/LifeCycle.java b/jooby/src/main/java/org/jooby/LifeCycle.java
index 50fefca9ee..fd1178b02a 100644
--- a/jooby/src/main/java/org/jooby/LifeCycle.java
+++ b/jooby/src/main/java/org/jooby/LifeCycle.java
@@ -207,6 +207,7 @@
 import org.jooby.funzy.Throwing;
 import org.jooby.funzy.Try;
 
+import javax.annotation.Nonnull;
 import javax.annotation.PostConstruct;
 import javax.annotation.PreDestroy;
 import java.lang.annotation.Annotation;
@@ -414,6 +415,7 @@ static Optional<Throwing.Consumer<Object>> lifeCycleAnnotation(final Class<?> ra
    * @param service Service type. Must be a singleton object.
    * @return This instance.
    */
+  @Nonnull
   default LifeCycle lifeCycle(final Class<?> service) {
     lifeCycleAnnotation(service, PostConstruct.class)
         .ifPresent(it -> onStart(app -> it.accept(app.require(service))));
@@ -434,6 +436,7 @@ default LifeCycle lifeCycle(final Class<?> service) {
    * @param task Task to run.
    * @return This env.
    */
+  @Nonnull
   LifeCycle onStart(Throwing.Consumer<Registry> task);
 
   /**
@@ -448,6 +451,7 @@ default LifeCycle lifeCycle(final Class<?> service) {
    * @param task Task to run.
    * @return This env.
    */
+  @Nonnull
   LifeCycle onStarted(Throwing.Consumer<Registry> task);
 
   /**
@@ -461,6 +465,7 @@ default LifeCycle lifeCycle(final Class<?> service) {
    * @param task Task to run.
    * @return This env.
    */
+  @Nonnull
   default LifeCycle onStart(final Throwing.Runnable task) {
     return onStart(app -> task.run());
   }
@@ -477,6 +482,7 @@ default LifeCycle onStart(final Throwing.Runnable task) {
    * @param task Task to run.
    * @return This env.
    */
+  @Nonnull
   default LifeCycle onStarted(final Throwing.Runnable task) {
     return onStarted(app -> task.run());
   }
@@ -492,6 +498,7 @@ default LifeCycle onStarted(final Throwing.Runnable task) {
    * @param task Task to run.
    * @return This env.
    */
+  @Nonnull
   default LifeCycle onStop(final Throwing.Runnable task) {
     return onStop(app -> task.run());
   }
@@ -507,6 +514,7 @@ default LifeCycle onStop(final Throwing.Runnable task) {
    * @param task Task to run.
    * @return This env.
    */
+  @Nonnull
   LifeCycle onStop(Throwing.Consumer<Registry> task);
 
 }
diff --git a/jooby/src/main/java/org/jooby/Mutant.java b/jooby/src/main/java/org/jooby/Mutant.java
index 877d3f8115..ea0983c277 100644
--- a/jooby/src/main/java/org/jooby/Mutant.java
+++ b/jooby/src/main/java/org/jooby/Mutant.java
@@ -213,6 +213,8 @@
 import com.google.inject.TypeLiteral;
 import com.google.inject.util.Types;
 
+import javax.annotation.Nonnull;
+
 /**
  * <p>
  * A type safe {@link Mutant} useful for reading parameters/headers/session attributes, etc..
@@ -338,6 +340,7 @@ default long longValue(final long value) {
   /**
    * @return Get a string when possible.
    */
+  @Nonnull
   default String value() {
     return to(String.class);
   }
@@ -346,6 +349,7 @@ default String value() {
    * @param value Default value to use.
    * @return Get a string.
    */
+  @Nonnull
   default String value(final String value) {
     return toOptional().orElse(value);
   }
@@ -385,6 +389,7 @@ default double doubleValue(final double value) {
    * @param <T> Enum type.
    * @return Get an enum when possible.
    */
+  @Nonnull
   default <T extends Enum<T>> T toEnum(final Class<T> type) {
     return to(type);
   }
@@ -395,6 +400,7 @@ default <T extends Enum<T>> T toEnum(final Class<T> type) {
    * @return Get an enum.
    */
   @SuppressWarnings("unchecked")
+  @Nonnull
   default <T extends Enum<T>> T toEnum(final T value) {
     Optional<T> optional = (Optional<T>) toOptional(value.getClass());
     return optional.orElse(value);
@@ -406,6 +412,7 @@ default <T extends Enum<T>> T toEnum(final T value) {
    * @return Get list of values when possible.
    */
   @SuppressWarnings("unchecked")
+  @Nonnull
   default <T> List<T> toList(final Class<T> type) {
     return (List<T>) to(TypeLiteral.get(Types.listOf(Primitives.wrap(type))));
   }
@@ -413,6 +420,7 @@ default <T> List<T> toList(final Class<T> type) {
   /**
    * @return Get list of values when possible.
    */
+  @Nonnull
   default List<String> toList() {
     return toList(String.class);
   }
@@ -420,6 +428,7 @@ default List<String> toList() {
   /**
    * @return Get set of values when possible.
    */
+  @Nonnull
   default Set<String> toSet() {
     return toSet(String.class);
   }
@@ -430,6 +439,7 @@ default Set<String> toSet() {
    * @return Get set of values when possible.
    */
   @SuppressWarnings("unchecked")
+  @Nonnull
   default <T> Set<T> toSet(final Class<T> type) {
     return (Set<T>) to(TypeLiteral.get(Types.setOf(Primitives.wrap(type))));
   }
@@ -437,6 +447,7 @@ default <T> Set<T> toSet(final Class<T> type) {
   /**
    * @return Get sorted set of values when possible.
    */
+  @Nonnull
   default SortedSet<String> toSortedSet() {
     return toSortedSet(String.class);
   }
@@ -447,6 +458,7 @@ default SortedSet<String> toSortedSet() {
    * @return Get sorted set of values when possible.
    */
   @SuppressWarnings("unchecked")
+  @Nonnull
   default <T extends Comparable<T>> SortedSet<T> toSortedSet(final Class<T> type) {
     return (SortedSet<T>) to(TypeLiteral.get(
         Types.newParameterizedType(SortedSet.class, Primitives.wrap(type))));
@@ -455,6 +467,7 @@ default <T extends Comparable<T>> SortedSet<T> toSortedSet(final Class<T> type)
   /**
    * @return An optional string value.
    */
+  @Nonnull
   default Optional<String> toOptional() {
     return toOptional(String.class);
   }
@@ -465,6 +478,7 @@ default Optional<String> toOptional() {
    * @return Get an optional value when possible.
    */
   @SuppressWarnings("unchecked")
+  @Nonnull
   default <T> Optional<T> toOptional(final Class<T> type) {
     return (Optional<T>) to(TypeLiteral.get(
         Types.newParameterizedType(Optional.class, Primitives.wrap(type))));
@@ -477,6 +491,7 @@ default <T> Optional<T> toOptional(final Class<T> type) {
    * @param <T> Target type.
    * @return Get a value when possible.
    */
+  @Nonnull
   default <T> T to(final Class<T> type) {
     return to(TypeLiteral.get(type));
   }
@@ -488,6 +503,7 @@ default <T> T to(final Class<T> type) {
    * @param <T> Target type.
    * @return Get a value when possible.
    */
+  @Nonnull
   <T> T to(TypeLiteral<T> type);
 
   /**
@@ -499,6 +515,7 @@ default <T> T to(final Class<T> type) {
    * @param <T> Target type.
    * @return Get a value when possible.
    */
+  @Nonnull
   default <T> T to(final Class<T> type, final String mtype) {
     return to(type, MediaType.valueOf(mtype));
   }
@@ -512,6 +529,7 @@ default <T> T to(final Class<T> type, final String mtype) {
    * @param <T> Target type.
    * @return Get a value when possible.
    */
+  @Nonnull
   default <T> T to(final Class<T> type, final MediaType mtype) {
     return to(TypeLiteral.get(type), mtype);
   }
@@ -525,6 +543,7 @@ default <T> T to(final Class<T> type, final MediaType mtype) {
    * @param <T> Target type.
    * @return Get a value when possible.
    */
+  @Nonnull
   default <T> T to(final TypeLiteral<T> type, final String mtype) {
     return to(type, MediaType.valueOf(mtype));
   }
@@ -538,6 +557,7 @@ default <T> T to(final TypeLiteral<T> type, final String mtype) {
    * @param <T> Target type.
    * @return Get a value when possible.
    */
+  @Nonnull
   <T> T to(TypeLiteral<T> type, MediaType mtype);
 
   /**
@@ -554,6 +574,7 @@ default <T> T to(final TypeLiteral<T> type, final String mtype) {
    *
    * @return A map view of this mutant.
    */
+  @Nonnull
   Map<String, Mutant> toMap();
 
   /**
diff --git a/jooby/src/main/java/org/jooby/Registry.java b/jooby/src/main/java/org/jooby/Registry.java
index 3386b3ee34..cd123bf0b7 100644
--- a/jooby/src/main/java/org/jooby/Registry.java
+++ b/jooby/src/main/java/org/jooby/Registry.java
@@ -207,6 +207,8 @@
 import com.google.inject.TypeLiteral;
 import com.google.inject.name.Names;
 
+import javax.annotation.Nonnull;
+
 /**
  * <h1>service registry</h1>
  * <p>
@@ -226,6 +228,7 @@ public interface Registry {
    * @param <T> Service type.
    * @return A ready to use object.
    */
+  @Nonnull
   default <T> T require(final Class<T> type) {
     return require(Key.get(type));
   }
@@ -238,6 +241,7 @@ default <T> T require(final Class<T> type) {
    * @param <T> Service type.
    * @return A ready to use object.
    */
+  @Nonnull
   default <T> T require(final String name, final Class<T> type) {
     return require(Key.get(type, Names.named(name)));
   }
@@ -249,6 +253,7 @@ default <T> T require(final String name, final Class<T> type) {
    * @param <T> Service type.
    * @return A ready to use object.
    */
+  @Nonnull
   default <T> T require(final TypeLiteral<T> type) {
     return require(Key.get(type));
   }
@@ -260,6 +265,7 @@ default <T> T require(final TypeLiteral<T> type) {
    * @param <T> Service type.
    * @return A ready to use object.
    */
+  @Nonnull
   <T> T require(Key<T> key);
 
 }
diff --git a/jooby/src/main/java/org/jooby/Request.java b/jooby/src/main/java/org/jooby/Request.java
index 9a93ad6275..eec1e70196 100644
--- a/jooby/src/main/java/org/jooby/Request.java
+++ b/jooby/src/main/java/org/jooby/Request.java
@@ -223,6 +223,8 @@
 import com.google.inject.Key;
 import com.google.inject.TypeLiteral;
 
+import javax.annotation.Nonnull;
+
 /**
  * Give you access at the current HTTP request in order to read parameters, headers and body.
  *
@@ -671,6 +673,7 @@ public static Request unwrap(final Request req) {
    *
    * @return The request URL pathname.
    */
+  @Nonnull
   default String path() {
     return path(false);
   }
@@ -680,6 +683,7 @@ default String path() {
    *
    * @return Raw path, like {@link #path()} but without decoding.
    */
+  @Nonnull
   String rawPath();
 
   /**
@@ -687,6 +691,7 @@ default String path() {
    *
    * @return The query string, without the leading <code>?</code>.
    */
+  @Nonnull
   Optional<String> queryString();
 
   /**
@@ -701,6 +706,7 @@ default String path() {
    * @param escape True if we want to escape this path.
    * @return The request URL pathname.
    */
+  @Nonnull
   default String path(final boolean escape) {
     String path = route().path();
     return escape ? UrlEscapers.urlFragmentEscaper().escape(path) : path;
@@ -712,11 +718,13 @@ default String path(final boolean escape) {
    *
    * @return Application context path..
    */
+  @Nonnull
   String contextPath();
 
   /**
    * @return HTTP method.
    */
+  @Nonnull
   default String method() {
     return route().method();
   }
@@ -724,11 +732,13 @@ default String method() {
   /**
    * @return The <code>Content-Type</code> header. Default is: {@literal*}/{@literal*}.
    */
+  @Nonnull
   MediaType type();
 
   /**
    * @return The value of the <code>Accept header</code>. Default is: {@literal*}/{@literal*}.
    */
+  @Nonnull
   List<MediaType> accept();
 
   /**
@@ -762,6 +772,7 @@ default String method() {
    * @param types Types to test.
    * @return The best acceptable type.
    */
+  @Nonnull
   default Optional<MediaType> accepts(final String... types) {
     return accepts(MediaType.valueOf(types));
   }
@@ -835,6 +846,7 @@ default boolean is(final List<MediaType> types) {
    * @param types Types to test.
    * @return The best acceptable type.
    */
+  @Nonnull
   default Optional<MediaType> accepts(final MediaType... types) {
     return accepts(ImmutableList.copyOf(types));
   }
@@ -870,6 +882,7 @@ default Optional<MediaType> accepts(final MediaType... types) {
    * @param types Types to test for.
    * @return The best acceptable type.
    */
+  @Nonnull
   Optional<MediaType> accepts(List<MediaType> types);
 
   /**
@@ -885,6 +898,7 @@ default Optional<MediaType> accepts(final MediaType... types) {
    *
    * @return All the parameters.
    */
+  @Nonnull
   Mutant params();
 
   /**
@@ -901,6 +915,7 @@ default Optional<MediaType> accepts(final MediaType... types) {
    * @param xss Xss filter to apply.
    * @return All the parameters.
    */
+  @Nonnull
   Mutant params(String... xss);
 
   /**
@@ -910,6 +925,7 @@ default Optional<MediaType> accepts(final MediaType... types) {
    * @param <T> Value type.
    * @return Instance of object.
    */
+  @Nonnull
   default <T> T params(final Class<T> type) {
     return params().to(type);
   }
@@ -921,6 +937,7 @@ default <T> T params(final Class<T> type) {
    * @param <T> Value type.
    * @return Instance of object.
    */
+  @Nonnull
   default <T> T form(final Class<T> type) {
     return params().to(type);
   }
@@ -933,6 +950,7 @@ default <T> T form(final Class<T> type) {
    * @param <T> Value type.
    * @return Instance of object.
    */
+  @Nonnull
   default <T> T params(final Class<T> type, final String... xss) {
     return params(xss).to(type);
   }
@@ -945,6 +963,7 @@ default <T> T params(final Class<T> type, final String... xss) {
    * @param <T> Value type.
    * @return Instance of object.
    */
+  @Nonnull
   default <T> T form(final Class<T> type, final String... xss) {
     return params(xss).to(type);
   }
@@ -976,6 +995,7 @@ default <T> T form(final Class<T> type, final String... xss) {
    * @param name A parameter's name.
    * @return A HTTP request parameter.
    */
+  @Nonnull
   Mutant param(String name);
 
   /**
@@ -1006,6 +1026,7 @@ default <T> T form(final Class<T> type, final String... xss) {
    * @param xss Xss filter to apply.
    * @return A HTTP request parameter.
    */
+  @Nonnull
   Mutant param(String name, String... xss);
 
   /**
@@ -1016,6 +1037,7 @@ default <T> T form(final Class<T> type, final String... xss) {
    * @return An {@link Upload}.
    * @throws IOException
    */
+  @Nonnull
   default Upload file(final String name) throws IOException {
     List<Upload> files = files(name);
     if (files.size() == 0) {
@@ -1032,6 +1054,7 @@ default Upload file(final String name) throws IOException {
    * @return An {@link Upload}.
    * @throws IOException
    */
+  @Nonnull
   default Optional<Upload> ifFile(final String name) throws IOException {
     List<Upload> files = files(name);
     return files.size() == 0 ? Optional.empty() : Optional.of(files.get(0));
@@ -1045,6 +1068,7 @@ default Optional<Upload> ifFile(final String name) throws IOException {
    * @return A list of {@link Upload}.
    * @throws IOException
    */
+  @Nonnull
   List<Upload> files(final String name) throws IOException;
 
   /**
@@ -1053,6 +1077,7 @@ default Optional<Upload> ifFile(final String name) throws IOException {
    * @param name A header's name.
    * @return A HTTP request header.
    */
+  @Nonnull
   Mutant header(String name);
 
   /**
@@ -1062,11 +1087,13 @@ default Optional<Upload> ifFile(final String name) throws IOException {
    * @param xss Xss escapers.
    * @return A HTTP request header.
    */
+  @Nonnull
   Mutant header(final String name, final String... xss);
 
   /**
    * @return All the headers.
    */
+  @Nonnull
   Map<String, Mutant> headers();
 
   /**
@@ -1075,11 +1102,13 @@ default Optional<Upload> ifFile(final String name) throws IOException {
    * @param name Cookie's name.
    * @return A cookie or an empty optional.
    */
+  @Nonnull
   Mutant cookie(String name);
 
   /**
    * @return All the cookies.
    */
+  @Nonnull
   List<Cookie> cookies();
 
   /**
@@ -1089,6 +1118,7 @@ default Optional<Upload> ifFile(final String name) throws IOException {
    * @return The HTTP body.
    * @throws Exception If body can't be converted or there is no HTTP body.
    */
+  @Nonnull
   Mutant body() throws Exception;
 
   /**
@@ -1102,6 +1132,7 @@ default Optional<Upload> ifFile(final String name) throws IOException {
    * @return Instance of object.
    * @throws Exception If body can't be converted or there is no HTTP body.
    */
+  @Nonnull
   default <T> T body(final Class<T> type) throws Exception {
     return body().to(type);
   }
@@ -1112,6 +1143,7 @@ default <T> T body(final Class<T> type) throws Exception {
    *
    * @return A current charset.
    */
+  @Nonnull
   Charset charset();
 
   /**
@@ -1119,6 +1151,7 @@ default <T> T body(final Class<T> type) throws Exception {
    *
    * @return A list of matching locales or empty list.
    */
+  @Nonnull
   default List<Locale> locales() {
     return locales(Locale::filter);
   }
@@ -1140,6 +1173,7 @@ default List<Locale> locales() {
    * @param filter A locale filter.
    * @return A list of matching locales.
    */
+  @Nonnull
   List<Locale> locales(BiFunction<List<Locale.LanguageRange>, List<Locale>, List<Locale>> filter);
 
   /**
@@ -1159,6 +1193,7 @@ default List<Locale> locales() {
    * @param filter A locale filter.
    * @return A matching locale.
    */
+  @Nonnull
   Locale locale(BiFunction<List<Locale.LanguageRange>, List<Locale>, Locale> filter);
 
   /**
@@ -1167,6 +1202,7 @@ default List<Locale> locales() {
    *
    * @return A matching locale.
    */
+  @Nonnull
   default Locale locale() {
     return locale((priorityList, locales) -> Optional.ofNullable(Locale.lookup(priorityList, locales))
         .orElse(locales.get(0)));
@@ -1181,6 +1217,7 @@ default Locale locale() {
   /**
    * @return The IP address of the client or last proxy that sent the request.
    */
+  @Nonnull
   String ip();
 
   /**
@@ -1192,6 +1229,7 @@ default Locale locale() {
   /**
    * @return The currently matched {@link Route}.
    */
+  @Nonnull
   Route route();
 
   /**
@@ -1200,17 +1238,20 @@ default Locale locale() {
    *
    * @return The fully qualified name of the server.
    */
+  @Nonnull
   String hostname();
 
   /**
    * @return The current session associated with this request or if the request does not have a
    *         session, creates one.
    */
+  @Nonnull
   Session session();
 
   /**
    * @return The current session associated with this request if there is one.
    */
+  @Nonnull
   Optional<Session> ifSession();
 
   /**
@@ -1227,6 +1268,7 @@ default boolean xhr() {
    * @return The name and version of the protocol the request uses in the form
    *         <i>protocol/majorVersion.minorVersion</i>, for example, HTTP/1.1
    */
+  @Nonnull
   String protocol();
 
   /**
@@ -1241,6 +1283,7 @@ default boolean xhr() {
    * @param value Attribute's local. NOT null.
    * @return This request.
    */
+  @Nonnull
   Request set(String name, Object value);
 
   /**
@@ -1264,6 +1307,7 @@ default boolean xhr() {
    * @return A mutable map with attributes from {@link FlashScope}.
    * @throws Err Bad request error if the {@link FlashScope} was not installed it.
    */
+  @Nonnull
   default Map<String, String> flash() throws Err {
     Optional<Map<String, String>> flash = ifGet(FlashScope.NAME);
     return flash.orElseThrow(() -> new Err(Status.BAD_REQUEST,
@@ -1280,6 +1324,7 @@ default Map<String, String> flash() throws Err {
    * @param value Attribute's value.
    * @return This request.
    */
+  @Nonnull
   default Request flash(final String name, final Object value) {
     requireNonNull(name, "Attribute's name is required.");
     Map<String, String> flash = flash();
@@ -1297,6 +1342,7 @@ default Request flash(final String name, final Object value) {
    * @param name Attribute's name.
    * @return Optional flash attribute.
    */
+  @Nonnull
   default Optional<String> ifFlash(final String name) {
     return Optional.ofNullable(flash().get(name));
   }
@@ -1308,6 +1354,7 @@ default Optional<String> ifFlash(final String name) {
    * @return Flash attribute.
    * @throws Err Bad request error if flash attribute is missing.
    */
+  @Nonnull
   default String flash(final String name) throws Err {
     return ifFlash(name)
         .orElseThrow(() -> new Err(Status.BAD_REQUEST,
@@ -1329,6 +1376,7 @@ default boolean isSet(final String name) {
    * @param <T> Target type.
    * @return A local attribute.
    */
+  @Nonnull
   <T> Optional<T> ifGet(String name);
 
   /**
@@ -1339,6 +1387,7 @@ default boolean isSet(final String name) {
    * @param <T> Target type.
    * @return A local attribute.
    */
+  @Nonnull
   default <T> T get(final String name, final T def) {
     Optional<T> opt = ifGet(name);
     return opt.orElse(def);
@@ -1352,6 +1401,7 @@ default <T> T get(final String name, final T def) {
    * @return A local attribute.
    * @throws Err with {@link Status#BAD_REQUEST}.
    */
+  @Nonnull
   default <T> T get(final String name) {
     Optional<T> opt = ifGet(name);
     return opt.orElseThrow(
@@ -1365,6 +1415,7 @@ default <T> T get(final String name) {
    * @param <T> Target type.
    * @return A local attribute.
    */
+  @Nonnull
   <T> Optional<T> unset(String name);
 
   /**
@@ -1372,6 +1423,7 @@ default <T> T get(final String name) {
    *
    * @return Attributes locals.
    */
+  @Nonnull
   Map<String, Object> attributes();
 
   /**
@@ -1381,6 +1433,7 @@ default <T> T get(final String name) {
    * @param value Actual object to bind.
    * @return Current request.
    */
+  @Nonnull
   default Request set(final Class<?> type, final Object value) {
     return set(TypeLiteral.get(type), value);
   }
@@ -1392,6 +1445,7 @@ default Request set(final Class<?> type, final Object value) {
    * @param value Actual object to bind.
    * @return Current request.
    */
+  @Nonnull
   default Request set(final TypeLiteral<?> type, final Object value) {
     return set(Key.get(type), value);
   }
@@ -1403,6 +1457,7 @@ default Request set(final TypeLiteral<?> type, final Object value) {
    * @param value Actual object to bind.
    * @return Current request.
    */
+  @Nonnull
   Request set(Key<?> key, Object value);
 
   /**
@@ -1411,6 +1466,7 @@ default Request set(final TypeLiteral<?> type, final Object value) {
    * @param path Path of the resource to push.
    * @return This request.
    */
+  @Nonnull
   default Request push(final String path) {
     return push(path, ImmutableMap.of());
   }
@@ -1422,6 +1478,7 @@ default Request push(final String path) {
    * @param headers Headers to send.
    * @return This request.
    */
+  @Nonnull
   Request push(final String path, final Map<String, Object> headers);
 
   /**
diff --git a/jooby/src/main/java/org/jooby/Response.java b/jooby/src/main/java/org/jooby/Response.java
index 66b9e9ff23..211f46d97e 100644
--- a/jooby/src/main/java/org/jooby/Response.java
+++ b/jooby/src/main/java/org/jooby/Response.java
@@ -215,6 +215,8 @@
 
 import com.google.common.collect.ImmutableList;
 
+import javax.annotation.Nonnull;
+
 /**
  * Give you access to the actual HTTP response. You can read/write headers and write HTTP body.
  *
@@ -496,6 +498,7 @@ default void download(final String filename, final File file) throws Throwable {
    * @param value A cookie's value.
    * @return This response.
    */
+  @Nonnull
   default Response cookie(final String name, final String value) {
     return cookie(new Cookie.Definition(name, value));
   }
@@ -506,6 +509,7 @@ default Response cookie(final String name, final String value) {
    * @param cookie A cookie definition.
    * @return This response.
    */
+  @Nonnull
   Response cookie(final Cookie.Definition cookie);
 
   /**
@@ -514,6 +518,7 @@ default Response cookie(final String name, final String value) {
    * @param cookie A cookie.
    * @return This response.
    */
+  @Nonnull
   Response cookie(Cookie cookie);
 
   /**
@@ -522,6 +527,7 @@ default Response cookie(final String name, final String value) {
    * @param name Cookie's name.
    * @return This response.
    */
+  @Nonnull
   Response clearCookie(String name);
 
   /**
@@ -530,6 +536,7 @@ default Response cookie(final String name, final String value) {
    * @param name A name.
    * @return A HTTP header.
    */
+  @Nonnull
   Mutant header(String name);
 
   /**
@@ -540,6 +547,7 @@ default Response cookie(final String name, final String value) {
    * @param value Header's value.
    * @return This response.
    */
+  @Nonnull
   Response header(String name, Object value);
 
   /**
@@ -550,6 +558,7 @@ default Response cookie(final String name, final String value) {
    * @param values Header's value.
    * @return This response.
    */
+  @Nonnull
   default Response header(final String name, final Object... values) {
     return header(name, ImmutableList.builder().add(values).build());
   }
@@ -562,6 +571,7 @@ default Response header(final String name, final Object... values) {
    * @param values Header's value.
    * @return This response.
    */
+  @Nonnull
   Response header(String name, Iterable<Object> values);
 
   /**
@@ -571,6 +581,7 @@ default Response header(final String name, final Object... values) {
    *
    * @return A current charset.
    */
+  @Nonnull
   Charset charset();
 
   /**
@@ -580,6 +591,7 @@ default Response header(final String name, final Object... values) {
    * @param charset A charset.
    * @return This response.
    */
+  @Nonnull
   Response charset(Charset charset);
 
   /**
@@ -588,11 +600,13 @@ default Response header(final String name, final Object... values) {
    * @param length Length of response.
    * @return This response.
    */
+  @Nonnull
   Response length(long length);
 
   /**
    * @return Get the response type.
    */
+  @Nonnull
   Optional<MediaType> type();
 
   /**
@@ -601,6 +615,7 @@ default Response header(final String name, final Object... values) {
    * @param type A media type.
    * @return This response.
    */
+  @Nonnull
   Response type(MediaType type);
 
   /**
@@ -609,6 +624,7 @@ default Response header(final String name, final Object... values) {
    * @param type A media type.
    * @return This response.
    */
+  @Nonnull
   default Response type(final String type) {
     return type(MediaType.valueOf(type));
   }
@@ -767,6 +783,7 @@ default void redirect(final String location) throws Throwable {
   /**
    * @return A HTTP status or empty if status was not set yet.
    */
+  @Nonnull
   Optional<Status> status();
 
   /**
@@ -775,6 +792,7 @@ default void redirect(final String location) throws Throwable {
    * @param status A HTTP status.
    * @return This response.
    */
+  @Nonnull
   Response status(Status status);
 
   /**
@@ -783,6 +801,7 @@ default void redirect(final String location) throws Throwable {
    * @param status A HTTP status.
    * @return This response.
    */
+  @Nonnull
   default Response status(final int status) {
     return status(Status.valueOf(status));
   }
diff --git a/jooby/src/main/java/org/jooby/Result.java b/jooby/src/main/java/org/jooby/Result.java
index 4ebb124771..b2d871acf2 100644
--- a/jooby/src/main/java/org/jooby/Result.java
+++ b/jooby/src/main/java/org/jooby/Result.java
@@ -215,6 +215,9 @@
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
 
+import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
+
 /**
  * Utility class for HTTP responses. Usually you start with a result {@link Results builder} and
  * then you customize (or not) one or more HTTP attribute.
@@ -336,6 +339,7 @@ protected Result clone() {
    * @param status A new response status to use.
    * @return This content.
    */
+  @Nonnull
   public Result status(final Status status) {
     this.status = requireNonNull(status, "A status is required.");
     return this;
@@ -347,6 +351,7 @@ public Result status(final Status status) {
    * @param status A new response status to use.
    * @return This content.
    */
+  @Nonnull
   public Result status(final int status) {
     return status(Status.valueOf(status));
   }
@@ -357,6 +362,7 @@ public Result status(final int status) {
    * @param type A content type.
    * @return This content.
    */
+  @Nonnull
   public Result type(final MediaType type) {
     this.type = requireNonNull(type, "A content type is required.");
     return this;
@@ -368,6 +374,7 @@ public Result type(final MediaType type) {
    * @param type A content type.
    * @return This content.
    */
+  @Nonnull
   public Result type(final String type) {
     return type(MediaType.valueOf(type));
   }
@@ -378,6 +385,7 @@ public Result type(final String type) {
    * @param content A result content.
    * @return This content.
    */
+  @Nonnull
   public Result set(final Object content) {
     this.value = content;
     return this;
@@ -390,6 +398,7 @@ public Result set(final Object content) {
    * @param supplier An object supplier.
    * @return This result.
    */
+  @Nonnull
   public Result when(final String type, final Supplier<Object> supplier) {
     return when(MediaType.valueOf(type), supplier);
   }
@@ -401,6 +410,7 @@ public Result when(final String type, final Supplier<Object> supplier) {
    * @param supplier An object supplier.
    * @return This result.
    */
+  @Nonnull
   public Result when(final MediaType type, final Supplier<Object> supplier) {
     return new ContentNegotiation(this).when(type, supplier);
   }
@@ -408,6 +418,7 @@ public Result when(final MediaType type, final Supplier<Object> supplier) {
   /**
    * @return headers for content.
    */
+  @Nonnull
   public Map<String, Object> headers() {
     return headers;
   }
@@ -415,6 +426,7 @@ public Map<String, Object> headers() {
   /**
    * @return Body status.
    */
+  @Nonnull
   public Optional<Status> status() {
     return Optional.ofNullable(status);
   }
@@ -422,6 +434,7 @@ public Optional<Status> status() {
   /**
    * @return Body type.
    */
+  @Nonnull
   public Optional<MediaType> type() {
     return Optional.ofNullable(type);
   }
@@ -431,6 +444,7 @@ public Optional<MediaType> type() {
    *
    * @return Value or <code>empty</code>
    */
+  @Nonnull
   public Optional<Object> ifGet() {
     return ifGet(MediaType.ALL);
   }
@@ -442,6 +456,7 @@ public Optional<Object> ifGet() {
    * @return Value or <code>null</code>
    */
   @SuppressWarnings("unchecked")
+  @Nullable
   public <T> T get() {
     return (T) value;
   }
@@ -452,6 +467,7 @@ public <T> T get() {
    * @param types Accept header.
    * @return Result content.
    */
+  @Nonnull
   public Optional<Object> ifGet(final List<MediaType> types) {
     return Optional.ofNullable(value);
   }
@@ -464,6 +480,7 @@ public Optional<Object> ifGet(final List<MediaType> types) {
    * @return Result content or <code>null</code>.
    */
   @SuppressWarnings("unchecked")
+  @Nullable
   public <T> T get(final List<MediaType> types) {
     return (T) value;
   }
@@ -476,6 +493,7 @@ public <T> T get(final List<MediaType> types) {
    * @param value Header's value.
    * @return This content.
    */
+  @Nonnull
   public Result header(final String name, final Object value) {
     requireNonNull(name, "Header's name is required.");
     requireNonNull(value, "Header's value is required.");
@@ -492,6 +510,7 @@ public Result header(final String name, final Object value) {
    * @param values Header's values.
    * @return This content.
    */
+  @Nonnull
   public Result header(final String name, final Object... values) {
     requireNonNull(name, "Header's name is required.");
     requireNonNull(values, "Header's values are required.");
@@ -507,6 +526,7 @@ public Result header(final String name, final Object... values) {
    * @param values Header's values.
    * @return This content.
    */
+  @Nonnull
   public Result header(final String name, final Iterable<Object> values) {
     requireNonNull(name, "Header's name is required.");
     requireNonNull(values, "Header's values are required.");
diff --git a/jooby/src/main/java/org/jooby/Results.java b/jooby/src/main/java/org/jooby/Results.java
index 92aa75e252..bf550cbafd 100644
--- a/jooby/src/main/java/org/jooby/Results.java
+++ b/jooby/src/main/java/org/jooby/Results.java
@@ -205,6 +205,7 @@
 
 import static java.util.Objects.requireNonNull;
 
+import javax.annotation.Nonnull;
 import java.util.function.Supplier;
 
 /**
@@ -221,6 +222,7 @@ public class Results {
    * @param entity A result value.
    * @return A new result.
    */
+  @Nonnull
   public static Result with(final Object entity) {
     return new Result().set(entity);
   }
@@ -232,6 +234,7 @@ public static Result with(final Object entity) {
    * @param status A HTTP status.
    * @return A new result.
    */
+  @Nonnull
   public static Result with(final Object entity, final Status status) {
     return new Result().status(status).set(entity);
   }
@@ -243,6 +246,7 @@ public static Result with(final Object entity, final Status status) {
    * @param status A HTTP status.
    * @return A new result.
    */
+  @Nonnull
   public static Result with(final Object entity, final int status) {
     return with(entity, Status.valueOf(status));
   }
@@ -253,6 +257,7 @@ public static Result with(final Object entity, final int status) {
    * @param status A status!
    * @return A new result.
    */
+  @Nonnull
   public static Result with(final Status status) {
     requireNonNull(status, "A HTTP status is required.");
     return new Result().status(status);
@@ -264,6 +269,7 @@ public static Result with(final Status status) {
    * @param status A status!
    * @return A new result.
    */
+  @Nonnull
   public static Result with(final int status) {
     requireNonNull(status, "A HTTP status is required.");
     return new Result().status(status);
@@ -272,6 +278,7 @@ public static Result with(final int status) {
   /**
    * @return A new result with {@link Status#OK}.
    */
+  @Nonnull
   public static Result ok() {
     return with(Status.OK);
   }
@@ -280,6 +287,7 @@ public static Result ok() {
    * @param view View to render.
    * @return A new view.
    */
+  @Nonnull
   public static View html(final String view) {
     return new View(view);
   }
@@ -288,6 +296,7 @@ public static View html(final String view) {
    * @param entity A result content!
    * @return A new json result.
    */
+  @Nonnull
   public static Result json(final Object entity) {
     return with(entity, 200).type(MediaType.json);
   }
@@ -296,6 +305,7 @@ public static Result json(final Object entity) {
    * @param entity A result content!
    * @return A new json result.
    */
+  @Nonnull
   public static Result xml(final Object entity) {
     return with(entity, 200).type(MediaType.xml);
   }
@@ -304,6 +314,7 @@ public static Result xml(final Object entity) {
    * @param entity A result content!
    * @return A new result with {@link Status#OK} and given content.
    */
+  @Nonnull
   public static Result ok(final Object entity) {
     return ok().set(entity);
   }
@@ -311,6 +322,7 @@ public static Result ok(final Object entity) {
   /**
    * @return A new result with {@link Status#ACCEPTED}.
    */
+  @Nonnull
   public static Result accepted() {
     return with(Status.ACCEPTED);
   }
@@ -319,6 +331,7 @@ public static Result accepted() {
    * @param content A result content!
    * @return A new result with {@link Status#ACCEPTED}.
    */
+  @Nonnull
   public static Result accepted(final Object content) {
     return accepted().set(content);
   }
@@ -326,6 +339,7 @@ public static Result accepted(final Object content) {
   /**
    * @return A new result with {@link Status#NO_CONTENT}.
    */
+  @Nonnull
   public static Result noContent() {
     return with(Status.NO_CONTENT);
   }
@@ -388,6 +402,7 @@ public static Result noContent() {
    * @param location A location.
    * @return A new result.
    */
+  @Nonnull
   public static Result redirect(final String location) {
     return redirect(Status.FOUND, location);
   }
@@ -450,6 +465,7 @@ public static Result redirect(final String location) {
    * @param location A location.
    * @return A new result.
    */
+  @Nonnull
   public static Result tempRedirect(final String location) {
     return redirect(Status.TEMPORARY_REDIRECT, location);
   }
@@ -512,6 +528,7 @@ public static Result tempRedirect(final String location) {
    * @param location A location.
    * @return A new result.
    */
+  @Nonnull
   public static Result moved(final String location) {
     return redirect(Status.MOVED_PERMANENTLY, location);
   }
@@ -574,6 +591,7 @@ public static Result moved(final String location) {
    * @param location A location.
    * @return A new result.
    */
+  @Nonnull
   public static Result seeOther(final String location) {
     return redirect(Status.SEE_OTHER, location);
   }
@@ -597,6 +615,7 @@ public static Result seeOther(final String location) {
    * @param supplier A result supplier.
    * @return A new result.
    */
+  @Nonnull
   public static Result when(final String type, final Supplier<Object> supplier) {
     return new Result().when(type, supplier);
   }
@@ -620,6 +639,7 @@ public static Result when(final String type, final Supplier<Object> supplier) {
    * @param supplier A result supplier.
    * @return A new result.
    */
+  @Nonnull
   public static Result when(final MediaType type, final Supplier<Object> supplier) {
     return new Result().when(type, supplier);
   }
diff --git a/jooby/src/main/java/org/jooby/Route.java b/jooby/src/main/java/org/jooby/Route.java
index 8869c20adb..0f8cd393d6 100644
--- a/jooby/src/main/java/org/jooby/Route.java
+++ b/jooby/src/main/java/org/jooby/Route.java
@@ -220,6 +220,8 @@
 import org.jooby.internal.SourceProvider;
 import org.jooby.funzy.Throwing;
 
+import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
 import java.lang.reflect.Array;
 import java.lang.reflect.Method;
 import java.util.ArrayList;
@@ -448,6 +450,7 @@ public String toString() {
     /**
      * @return Class where the route
      */
+    @Nonnull
     Optional<String> declaringClass();
   }
 
@@ -520,6 +523,7 @@ interface Mapper<T> {
      * @return A new mapper.
      */
     @SuppressWarnings({"rawtypes", "unchecked"})
+    @Nonnull
     static Mapper<Object> chain(final Mapper it, final Mapper next) {
       return create(it.name() + ">" + next.name(), v -> next.map(it.map(v)));
     }
@@ -532,6 +536,7 @@ static Mapper<Object> chain(final Mapper it, final Mapper next) {
      * @param <T> Value type.
      * @return A new mapper.
      */
+    @Nonnull
     static <T> Mapper<T> create(final String name, final Throwing.Function<T, Object> fn) {
       return new Route.Mapper<T>() {
         @Override
@@ -554,6 +559,7 @@ public String toString() {
     /**
      * @return Mapper's name.
      */
+    @Nonnull
     default String name() {
       String name = Optional.ofNullable(Strings.emptyToNull(getClass().getSimpleName()))
           .orElseGet(() -> {
@@ -570,6 +576,7 @@ default String name() {
      * @return Mapped value.
      * @throws Throwable If mapping fails.
      */
+    @Nonnull
     Object map(T value) throws Throwable;
   }
 
@@ -590,6 +597,7 @@ interface Props<T extends Props<T>> {
      * @param value Attribute's value.
      * @return This instance.
      */
+    @Nonnull
     T attr(String name, Object value);
 
     /**
@@ -598,6 +606,7 @@ interface Props<T extends Props<T>> {
      * @param name A renderer's name.
      * @return This instance.
      */
+    @Nonnull
     T renderer(final String name);
 
     /**
@@ -605,6 +614,7 @@ interface Props<T extends Props<T>> {
      *
      * @return Explicit renderer to use or <code>null</code>.
      */
+    @Nullable
     String renderer();
 
     /**
@@ -615,6 +625,7 @@ interface Props<T extends Props<T>> {
      * @param name A route's name.
      * @return This instance.
      */
+    @Nonnull
     T name(final String name);
 
     /**
@@ -623,6 +634,7 @@ interface Props<T extends Props<T>> {
      * @param consumes The media types to test for.
      * @return This instance.
      */
+    @Nonnull
     default T consumes(final MediaType... consumes) {
       return consumes(Arrays.asList(consumes));
     }
@@ -633,6 +645,7 @@ default T consumes(final MediaType... consumes) {
      * @param consumes The media types to test for.
      * @return This instance.
      */
+    @Nonnull
     default T consumes(final String... consumes) {
       return consumes(MediaType.valueOf(consumes));
     }
@@ -643,6 +656,7 @@ default T consumes(final String... consumes) {
      * @param consumes The media types to test for.
      * @return This instance.
      */
+    @Nonnull
     T consumes(final List<MediaType> consumes);
 
     /**
@@ -651,6 +665,7 @@ default T consumes(final String... consumes) {
      * @param produces The media types to test for.
      * @return This instance.
      */
+    @Nonnull
     default T produces(final MediaType... produces) {
       return produces(Arrays.asList(produces));
     }
@@ -661,6 +676,7 @@ default T produces(final MediaType... produces) {
      * @param produces The media types to test for.
      * @return This instance.
      */
+    @Nonnull
     default T produces(final String... produces) {
       return produces(MediaType.valueOf(produces));
     }
@@ -671,6 +687,7 @@ default T produces(final String... produces) {
      * @param produces The media types to test for.
      * @return This instance.
      */
+    @Nonnull
     T produces(final List<MediaType> produces);
 
     /**
@@ -687,6 +704,7 @@ default T produces(final String... produces) {
      * @param excludes A path pattern.
      * @return This instance.
      */
+    @Nonnull
     default T excludes(final String... excludes) {
       return excludes(Arrays.asList(excludes));
     }
@@ -705,8 +723,10 @@ default T excludes(final String... excludes) {
      * @param excludes A path pattern.
      * @return This instance.
      */
+    @Nonnull
     T excludes(final List<String> excludes);
 
+    @Nonnull
     T map(Mapper<?> mapper);
   }
 
@@ -754,41 +774,49 @@ public List<Route.Definition> routes() {
     // ********************************************************************************************
     // ALL
     // ********************************************************************************************
+    @Nonnull
     public Group all(final String pattern, final Route.Filter filter) {
       newRoute("*", pattern, filter);
       return this;
     }
 
+    @Nonnull
     public Group all(final String pattern, final Route.Handler handler) {
       newRoute("*", pattern, handler);
       return this;
     }
 
+    @Nonnull
     public Group all(final String pattern, final Route.OneArgHandler handler) {
       newRoute("*", pattern, handler);
       return this;
     }
 
+    @Nonnull
     public Group all(final String pattern, final Route.ZeroArgHandler handler) {
       newRoute("*", pattern, handler);
       return this;
     }
 
+    @Nonnull
     public Group all(final Route.Filter filter) {
       newRoute("*", "", filter);
       return this;
     }
 
+    @Nonnull
     public Group all(final Route.Handler handler) {
       newRoute("*", "", handler);
       return this;
     }
 
+    @Nonnull
     public Group all(final Route.OneArgHandler handler) {
       newRoute("*", "", handler);
       return this;
     }
 
+    @Nonnull
     public Group all(final Route.ZeroArgHandler handler) {
       newRoute("*", "", handler);
       return this;
@@ -797,41 +825,49 @@ public Group all(final Route.ZeroArgHandler handler) {
     // ********************************************************************************************
     // GET
     // ********************************************************************************************
+    @Nonnull
     public Group get(final String pattern, final Route.Filter filter) {
       newRoute(GET, pattern, filter);
       return this;
     }
 
+    @Nonnull
     public Group get(final String pattern, final Route.Handler handler) {
       newRoute(GET, pattern, handler);
       return this;
     }
 
+    @Nonnull
     public Group get(final String pattern, final Route.OneArgHandler handler) {
       newRoute(GET, pattern, handler);
       return this;
     }
 
+    @Nonnull
     public Group get(final String pattern, final Route.ZeroArgHandler handler) {
       newRoute(GET, pattern, handler);
       return this;
     }
 
+    @Nonnull
     public Group get(final Route.Filter filter) {
       newRoute(GET, "", filter);
       return this;
     }
 
+    @Nonnull
     public Group get(final Route.Handler handler) {
       newRoute(GET, "", handler);
       return this;
     }
 
+    @Nonnull
     public Group get(final Route.OneArgHandler handler) {
       newRoute(GET, "", handler);
       return this;
     }
 
+    @Nonnull
     public Group get(final Route.ZeroArgHandler handler) {
       newRoute(GET, "", handler);
       return this;
@@ -840,41 +876,49 @@ public Group get(final Route.ZeroArgHandler handler) {
     // ********************************************************************************************
     // POST
     // ********************************************************************************************
+    @Nonnull
     public Group post(final String pattern, final Route.Filter filter) {
       newRoute(POST, pattern, filter);
       return this;
     }
 
+    @Nonnull
     public Group post(final String pattern, final Route.Handler handler) {
       newRoute(POST, pattern, handler);
       return this;
     }
 
+    @Nonnull
     public Group post(final String pattern, final Route.OneArgHandler handler) {
       newRoute(POST, pattern, handler);
       return this;
     }
 
+    @Nonnull
     public Group post(final String pattern, final Route.ZeroArgHandler handler) {
       newRoute(POST, pattern, handler);
       return this;
     }
 
+    @Nonnull
     public Group post(final Route.Filter filter) {
       newRoute(POST, "", filter);
       return this;
     }
 
+    @Nonnull
     public Group post(final Route.Handler handler) {
       newRoute(POST, "", handler);
       return this;
     }
 
+    @Nonnull
     public Group post(final Route.OneArgHandler handler) {
       newRoute(POST, "", handler);
       return this;
     }
 
+    @Nonnull
     public Group post(final Route.ZeroArgHandler handler) {
       newRoute(POST, "", handler);
       return this;
@@ -883,41 +927,49 @@ public Group post(final Route.ZeroArgHandler handler) {
     // ********************************************************************************************
     // PUT
     // ********************************************************************************************
+    @Nonnull
     public Group put(final String pattern, final Route.Filter filter) {
       newRoute(PUT, pattern, filter);
       return this;
     }
 
+    @Nonnull
     public Group put(final String pattern, final Route.Handler handler) {
       newRoute(PUT, pattern, handler);
       return this;
     }
 
+    @Nonnull
     public Group put(final String pattern, final Route.OneArgHandler handler) {
       newRoute(PUT, pattern, handler);
       return this;
     }
 
+    @Nonnull
     public Group put(final String pattern, final Route.ZeroArgHandler handler) {
       newRoute(PUT, pattern, handler);
       return this;
     }
 
+    @Nonnull
     public Group put(final Route.Filter filter) {
       newRoute(PUT, "", filter);
       return this;
     }
 
+    @Nonnull
     public Group put(final Route.Handler handler) {
       newRoute(PUT, "", handler);
       return this;
     }
 
+    @Nonnull
     public Group put(final Route.OneArgHandler handler) {
       newRoute(PUT, "", handler);
       return this;
     }
 
+    @Nonnull
     public Group put(final Route.ZeroArgHandler handler) {
       newRoute(PUT, "", handler);
       return this;
@@ -926,41 +978,49 @@ public Group put(final Route.ZeroArgHandler handler) {
     // ********************************************************************************************
     // DELETE
     // ********************************************************************************************
+    @Nonnull
     public Group delete(final String pattern, final Route.Filter filter) {
       newRoute(DELETE, pattern, filter);
       return this;
     }
 
+    @Nonnull
     public Group delete(final String pattern, final Route.Handler handler) {
       newRoute(DELETE, pattern, handler);
       return this;
     }
 
+    @Nonnull
     public Group delete(final String pattern, final Route.OneArgHandler handler) {
       newRoute(DELETE, pattern, handler);
       return this;
     }
 
+    @Nonnull
     public Group delete(final String pattern, final Route.ZeroArgHandler handler) {
       newRoute(DELETE, pattern, handler);
       return this;
     }
 
+    @Nonnull
     public Group delete(final Route.Filter filter) {
       newRoute(DELETE, "", filter);
       return this;
     }
 
+    @Nonnull
     public Group delete(final Route.Handler handler) {
       newRoute(DELETE, "", handler);
       return this;
     }
 
+    @Nonnull
     public Group delete(final Route.OneArgHandler handler) {
       newRoute(DELETE, "", handler);
       return this;
     }
 
+    @Nonnull
     public Group delete(final Route.ZeroArgHandler handler) {
       newRoute(DELETE, "", handler);
       return this;
@@ -969,41 +1029,49 @@ public Group delete(final Route.ZeroArgHandler handler) {
     // ********************************************************************************************
     // PATCH
     // ********************************************************************************************
+    @Nonnull
     public Group patch(final String pattern, final Route.Filter filter) {
       newRoute(PATCH, pattern, filter);
       return this;
     }
 
+    @Nonnull
     public Group patch(final String pattern, final Route.Handler handler) {
       newRoute(PATCH, pattern, handler);
       return this;
     }
 
+    @Nonnull
     public Group patch(final String pattern, final Route.OneArgHandler handler) {
       newRoute(PATCH, pattern, handler);
       return this;
     }
 
+    @Nonnull
     public Group patch(final String pattern, final Route.ZeroArgHandler handler) {
       newRoute(PATCH, pattern, handler);
       return this;
     }
 
+    @Nonnull
     public Group patch(final Route.Filter filter) {
       newRoute(PATCH, "", filter);
       return this;
     }
 
+    @Nonnull
     public Group patch(final Route.Handler handler) {
       newRoute(PATCH, "", handler);
       return this;
     }
 
+    @Nonnull
     public Group patch(final Route.OneArgHandler handler) {
       newRoute(PATCH, "", handler);
       return this;
     }
 
+    @Nonnull
     public Group patch(final Route.ZeroArgHandler handler) {
       newRoute(PATCH, "", handler);
       return this;
@@ -1016,6 +1084,7 @@ public Group patch(final Route.ZeroArgHandler handler) {
      * @return This instance.
      */
     @Override
+    @Nonnull
     public Group name(final String name) {
       for (Definition definition : routes) {
         if (prefix != null) {
@@ -1028,6 +1097,7 @@ public Group name(final String name) {
     }
 
     @Override
+    @Nonnull
     public Group consumes(final List<MediaType> types) {
       for (Definition definition : routes) {
         definition.consumes(types);
@@ -1036,6 +1106,7 @@ public Group consumes(final List<MediaType> types) {
     }
 
     @Override
+    @Nonnull
     public Group produces(final List<MediaType> types) {
       for (Definition definition : routes) {
         definition.produces(types);
@@ -1044,6 +1115,7 @@ public Group produces(final List<MediaType> types) {
     }
 
     @Override
+    @Nonnull
     public Group attr(final String name, final Object value) {
       for (Definition definition : routes) {
         definition.attr(name, value);
@@ -1052,6 +1124,7 @@ public Group attr(final String name, final Object value) {
     }
 
     @Override
+    @Nonnull
     public Group excludes(final List<String> excludes) {
       for (Definition definition : routes) {
         definition.excludes(excludes);
@@ -1060,6 +1133,7 @@ public Group excludes(final List<String> excludes) {
     }
 
     @Override
+    @Nonnull
     public Group map(final Mapper<?> mapper) {
       for (Definition definition : routes) {
         definition.map(mapper);
@@ -1383,11 +1457,12 @@ public Definition(final String method, final String pattern,
      *
      * @return A path pattern.
      */
+    @Nonnull
     public String pattern() {
       return pattern;
     }
 
-    @Override
+    @Nonnull
     public String renderer() {
       return renderer;
     }
@@ -1401,6 +1476,7 @@ public Definition renderer(final String name) {
     /**
      * @return List of path variables (if any).
      */
+    @Nonnull
     public List<String> vars() {
       return cpattern.vars();
     }
@@ -1412,6 +1488,7 @@ public List<String> vars() {
      * @return Indicates if the {@link #pattern()} contains a glob charecter, like <code>?</code>,
      *         <code>*</code> or <code>**</code>.
      */
+    @Nonnull
     public boolean glob() {
       return cpattern.glob();
     }
@@ -1421,6 +1498,7 @@ public boolean glob() {
      *
      * @return Source information (where the route was defined).
      */
+    @Nonnull
     public Route.Source source() {
       return new RouteSourceImpl(declaringClass, line);
     }
@@ -1431,6 +1509,7 @@ public Route.Source source() {
      * @param vars Path variables.
      * @return A route pattern.
      */
+    @Nonnull
     public String reverse(final Map<String, Object> vars) {
       return cpattern.reverse(vars);
     }
@@ -1441,11 +1520,13 @@ public String reverse(final Map<String, Object> vars) {
      * @param values Path variable values.
      * @return A route pattern.
      */
+    @Nonnull
     public String reverse(final Object... values) {
       return cpattern.reverse(values);
     }
 
     @Override
+    @Nonnull
     public Definition attr(final String name, final Object value) {
       requireNonNull(name, "Attribute name is required.");
       requireNonNull(value, "Attribute value is required.");
@@ -1480,6 +1561,7 @@ private boolean valid(final Object value) {
      * @return Attribute's value or <code>null</code>.
      */
     @SuppressWarnings("unchecked")
+    @Nonnull
     public <T> T attr(final String name) {
       return (T) attributes.get(name);
     }
@@ -1487,6 +1569,7 @@ public <T> T attr(final String name) {
     /**
      * @return A read only view of attributes.
      */
+    @Nonnull
     public Map<String, Object> attributes() {
       return attributes;
     }
@@ -1500,6 +1583,7 @@ public Map<String, Object> attributes() {
      * @param accept The <code>Accept</code> header.
      * @return A route or an empty optional.
      */
+    @Nonnull
     public Optional<Route> matches(final String method,
         final String path, final MediaType contentType,
         final List<MediaType> accept) {
@@ -1524,6 +1608,7 @@ public Optional<Route> matches(final String method,
     /**
      * @return HTTP method or <code>*</code>.
      */
+    @Nonnull
     public String method() {
       return method;
     }
@@ -1531,6 +1616,7 @@ public String method() {
     /**
      * @return Handler behind this route.
      */
+    @Nonnull
     public Route.Filter filter() {
       return filter;
     }
@@ -1541,6 +1627,7 @@ public Route.Filter filter() {
      *
      * @return Route name. Default is: <code>anonymous</code>.
      */
+    @Nonnull
     public String name() {
       return name;
     }
@@ -1554,6 +1641,7 @@ public String name() {
      * @return This definition.
      */
     @Override
+    @Nonnull
     public Definition name(final String name) {
       checkArgument(!Strings.isNullOrEmpty(name), "A route's name is required.");
       this.name = normalize(prefix != null ? prefix + "/" + name : name);
@@ -1645,6 +1733,7 @@ public Definition excludes(final List<String> excludes) {
     /**
      * @return List of exclusion filters (if any).
      */
+    @Nonnull
     public List<String> excludes() {
       return excludes.stream().map(r -> r.pattern()).collect(Collectors.toList());
     }
@@ -1661,6 +1750,7 @@ private boolean excludes(final String path) {
     /**
      * @return All the types this route can consumes.
      */
+    @Nonnull
     public List<MediaType> consumes() {
       return Collections.unmodifiableList(this.consumes);
     }
@@ -1668,11 +1758,13 @@ public List<MediaType> consumes() {
     /**
      * @return All the types this route can produces.
      */
+    @Nonnull
     public List<MediaType> produces() {
       return Collections.unmodifiableList(this.produces);
     }
 
     @Override
+    @Nonnull
     public Definition map(final Mapper<?> mapper) {
       this.mapper = requireNonNull(mapper, "Mapper is required.");
       return this;
@@ -1684,6 +1776,7 @@ public Definition map(final Mapper<?> mapper) {
      * @param line Line number.
      * @return This instance.
      */
+    @Nonnull
     public Definition line(final int line) {
       this.line = line;
       return this;
@@ -1695,6 +1788,7 @@ public Definition line(final int line) {
      * @param declaringClass A source class.
      * @return This instance.
      */
+    @Nonnull
     public Definition declaringClass(final String declaringClass) {
       this.declaringClass = declaringClass;
       return this;
@@ -1976,6 +2070,7 @@ interface MethodHandler extends Handler {
      *
      * @return Target method.
      */
+    @Nonnull
     Method method();
 
     /**
@@ -1983,6 +2078,7 @@ interface MethodHandler extends Handler {
      *
      * @return Target class.
      */
+    @Nonnull
     Class<?> implementingClass();
   }
 
@@ -2426,16 +2522,19 @@ default void next(final Request req, final Response rsp) throws Throwable {
   /**
    * @return Current request path.
    */
+  @Nonnull
   String path();
 
   /**
    * @return Current HTTP method.
    */
+  @Nonnull
   String method();
 
   /**
    * @return The currently matched pattern.
    */
+  @Nonnull
   String pattern();
 
   /**
@@ -2444,6 +2543,7 @@ default void next(final Request req, final Response rsp) throws Throwable {
    *
    * @return Route name, defaults to <code>"anonymous"</code>
    */
+  @Nonnull
   String name();
 
   /**
@@ -2457,16 +2557,19 @@ default void next(final Request req, final Response rsp) throws Throwable {
    *
    * @return The currently matched path variables (if any).
    */
+  @Nonnull
   Map<Object, String> vars();
 
   /**
    * @return List all the types this route can consumes, defaults is: {@code * / *}.
    */
+  @Nonnull
   List<MediaType> consumes();
 
   /**
    * @return List all the types this route can produces, defaults is: {@code * / *}.
    */
+  @Nonnull
   List<MediaType> produces();
 
   /**
@@ -2483,6 +2586,7 @@ default boolean apply(final String prefix) {
   /**
    * @return All the available attributes in the execution chain.
    */
+  @Nonnull
   Map<String, Object> attributes();
 
   /**
@@ -2493,6 +2597,7 @@ default boolean apply(final String prefix) {
    * @return Attribute value.
    */
   @SuppressWarnings("unchecked")
+  @Nonnull
   default <T> T attr(final String name) {
     return (T) attributes().get(name);
   }
@@ -2502,6 +2607,7 @@ default <T> T attr(final String name) {
    *
    * @return Explicit renderer to use or <code>null</code>.
    */
+  @Nonnull
   String renderer();
 
   /**
@@ -2519,6 +2625,7 @@ default <T> T attr(final String name) {
    * @param vars Path variables.
    * @return A route pattern.
    */
+  @Nonnull
   String reverse(final Map<String, Object> vars);
 
   /**
@@ -2527,6 +2634,7 @@ default <T> T attr(final String name) {
    * @param values Path variable values.
    * @return A route pattern.
    */
+  @Nonnull
   String reverse(final Object... values);
 
   /**
@@ -2535,6 +2643,7 @@ default <T> T attr(final String name) {
    * @param path A path to normalize.
    * @return A normalized path.
    */
+  @Nonnull
   static String normalize(final String path) {
     return RoutePattern.normalize(path);
   }
@@ -2545,6 +2654,7 @@ static String normalize(final String path) {
    * @param path Path.
    * @return Original path.
    */
+  @Nonnull
   static String unerrpath(final String path) {
     if (path.charAt(0) == OUT_OF_PATH) {
       return path.substring(1);
@@ -2558,6 +2668,7 @@ static String unerrpath(final String path) {
    * @param path Path.
    * @return Invalid path.
    */
+  @Nonnull
   static String errpath(final String path) {
     return OUT_OF_PATH + path;
   }
@@ -2567,6 +2678,7 @@ static String errpath(final String path) {
    *
    * @return Source information (where the route was defined).
    */
+  @Nonnull
   Route.Source source();
 
   /**
@@ -2575,6 +2687,7 @@ static String errpath(final String path) {
    * @param indent Indent level
    * @return Output.
    */
+  @Nonnull
   default String print(final int indent) {
     StringBuilder buff = new StringBuilder();
     String[] header = {"Method", "Path", "Source", "Name", "Pattern", "Consumes", "Produces"};
@@ -2604,6 +2717,7 @@ default String print(final int indent) {
    *
    * @return Output.
    */
+  @Nonnull
   default String print() {
     return print(0);
   }
diff --git a/jooby/src/main/java/org/jooby/Router.java b/jooby/src/main/java/org/jooby/Router.java
index b8096ccd2e..abe69645b5 100644
--- a/jooby/src/main/java/org/jooby/Router.java
+++ b/jooby/src/main/java/org/jooby/Router.java
@@ -211,6 +211,8 @@
 import org.jooby.Route.Mapper;
 import org.jooby.handlers.AssetHandler;
 
+import javax.annotation.Nonnull;
+
 /**
  * Route DSL. Constructs and creates several flavors of jooby routes.
  *
@@ -226,6 +228,7 @@ public interface Router {
    * @param app Routes provider.
    * @return This jooby instance.
    */
+  @Nonnull
   Router use(final Jooby app);
 
   /**
@@ -236,6 +239,7 @@ public interface Router {
    * @param app Routes provider.
    * @return This jooby instance.
    */
+  @Nonnull
   Router use(final String path, final Jooby app);
 
   /**
@@ -252,6 +256,7 @@ public interface Router {
    * @param pattern Global pattern to use.
    * @return A route namespace.
    */
+  @Nonnull
   Route.Group use(String pattern);
 
   /**
@@ -261,6 +266,7 @@ public interface Router {
    * @param filter A filter to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Definition use(String path, Route.Filter filter);
 
   /**
@@ -271,6 +277,7 @@ public interface Router {
    * @param filter A filter to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Definition use(String method, String path, Route.Filter filter);
 
   /**
@@ -283,6 +290,7 @@ public interface Router {
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Definition use(String method, String path, Route.Handler handler);
 
   /**
@@ -294,6 +302,7 @@ public interface Router {
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Definition use(String path, Route.Handler handler);
 
   /**
@@ -303,6 +312,7 @@ public interface Router {
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Definition use(String path, Route.OneArgHandler handler);
 
   /**
@@ -318,6 +328,7 @@ public interface Router {
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Definition get(String path, Route.Handler handler);
 
   /**
@@ -334,6 +345,7 @@ public interface Router {
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Collection get(String path1, String path2, Route.Handler handler);
 
   /**
@@ -351,6 +363,7 @@ public interface Router {
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Collection get(String path1, String path2, String path3, Route.Handler handler);
 
   /**
@@ -366,6 +379,7 @@ public interface Router {
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Definition get(String path, Route.OneArgHandler handler);
 
   /**
@@ -382,6 +396,7 @@ public interface Router {
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Collection get(String path1, String path2, Route.OneArgHandler handler);
 
   /**
@@ -399,6 +414,7 @@ public interface Router {
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Collection get(String path1, String path2, String path3, Route.OneArgHandler handler);
 
   /**
@@ -414,6 +430,7 @@ public interface Router {
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Definition get(String path, Route.ZeroArgHandler handler);
 
   /**
@@ -430,6 +447,7 @@ public interface Router {
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Collection get(String path1, String path2, Route.ZeroArgHandler handler);
 
   /**
@@ -447,6 +465,7 @@ public interface Router {
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Collection get(String path1, String path2, String path3, Route.ZeroArgHandler handler);
 
   /**
@@ -462,6 +481,7 @@ public interface Router {
    * @param filter A filter to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Definition get(String path, Route.Filter filter);
 
   /**
@@ -479,6 +499,7 @@ public interface Router {
    * @param filter A filter to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Collection get(String path1, String path2, Route.Filter filter);
 
   /**
@@ -496,6 +517,7 @@ public interface Router {
    * @param filter A filter to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Collection get(String path1, String path2, String path3, Route.Filter filter);
 
   /**
@@ -511,6 +533,7 @@ public interface Router {
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Definition post(String path, Route.Handler handler);
 
   /**
@@ -527,6 +550,7 @@ public interface Router {
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Collection post(String path1, String path2, Route.Handler handler);
 
   /**
@@ -544,6 +568,7 @@ public interface Router {
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Collection post(String path1, String path2, String path3, Route.Handler handler);
 
   /**
@@ -559,6 +584,7 @@ public interface Router {
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Definition post(String path, Route.OneArgHandler handler);
 
   /**
@@ -575,6 +601,7 @@ public interface Router {
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Collection post(String path1, String path2, Route.OneArgHandler handler);
 
   /**
@@ -592,6 +619,7 @@ public interface Router {
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Collection post(String path1, String path2, String path3, Route.OneArgHandler handler);
 
   /**
@@ -607,6 +635,7 @@ public interface Router {
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Definition post(String path, Route.ZeroArgHandler handler);
 
   /**
@@ -623,6 +652,7 @@ public interface Router {
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Collection post(String path1, String path2, Route.ZeroArgHandler handler);
 
   /**
@@ -640,6 +670,7 @@ public interface Router {
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Collection post(String path1, String path2, String path3, Route.ZeroArgHandler handler);
 
   /**
@@ -655,6 +686,7 @@ public interface Router {
    * @param filter A filter to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Definition post(String path, Route.Filter filter);
 
   /**
@@ -671,6 +703,7 @@ public interface Router {
    * @param filter A filter to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Collection post(String path1, String path2, Route.Filter filter);
 
   /**
@@ -688,6 +721,7 @@ public interface Router {
    * @param filter A filter to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Collection post(String path1, String path2, String path3, Route.Filter filter);
 
   /**
@@ -703,6 +737,7 @@ public interface Router {
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Definition head(String path, Route.Handler handler);
 
   /**
@@ -718,6 +753,7 @@ public interface Router {
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Definition head(String path, Route.OneArgHandler handler);
 
   /**
@@ -733,6 +769,7 @@ public interface Router {
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Definition head(String path, Route.ZeroArgHandler handler);
 
   /**
@@ -748,6 +785,7 @@ public interface Router {
    * @param filter A filter to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Definition head(String path, Route.Filter filter);
 
   /**
@@ -761,6 +799,7 @@ public interface Router {
    *
    * @return A new route definition.
    */
+  @Nonnull
   Route.Definition head();
 
   /**
@@ -776,6 +815,7 @@ public interface Router {
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Definition options(String path, Route.Handler handler);
 
   /**
@@ -791,6 +831,7 @@ public interface Router {
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Definition options(String path, Route.OneArgHandler handler);
 
   /**
@@ -806,6 +847,7 @@ public interface Router {
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Definition options(String path, Route.ZeroArgHandler handler);
 
   /**
@@ -822,6 +864,7 @@ public interface Router {
    * @param filter A callback to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Definition options(String path, Route.Filter filter);
 
   /**
@@ -843,6 +886,7 @@ public interface Router {
    *
    * @return A new route definition.
    */
+  @Nonnull
   Route.Definition options();
 
   /**
@@ -858,6 +902,7 @@ public interface Router {
    * @param handler A route to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Definition put(String path, Route.Handler handler);
 
   /**
@@ -874,6 +919,7 @@ public interface Router {
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Collection put(String path1, String path2, Route.Handler handler);
 
   /**
@@ -891,6 +937,7 @@ public interface Router {
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Collection put(String path1, String path2, String path3, Route.Handler handler);
 
   /**
@@ -906,6 +953,7 @@ public interface Router {
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Definition put(String path, Route.OneArgHandler handler);
 
   /**
@@ -922,6 +970,7 @@ public interface Router {
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Collection put(String path1, String path2,
       Route.OneArgHandler handler);
 
@@ -942,6 +991,7 @@ Route.Collection put(String path1, String path2,
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Collection put(String path1, String path2, String path3, Route.OneArgHandler handler);
 
   /**
@@ -957,6 +1007,7 @@ Route.Collection put(String path1, String path2,
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Definition put(String path, Route.ZeroArgHandler handler);
 
   /**
@@ -975,6 +1026,7 @@ Route.Collection put(String path1, String path2,
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Collection put(String path1, String path2, Route.ZeroArgHandler handler);
 
   /**
@@ -994,6 +1046,7 @@ Route.Collection put(String path1, String path2,
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Collection put(String path1, String path2, String path3, Route.ZeroArgHandler handler);
 
   /**
@@ -1009,6 +1062,7 @@ Route.Collection put(String path1, String path2,
    * @param filter A callback to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Definition put(String path, Route.Filter filter);
 
   /**
@@ -1025,6 +1079,7 @@ Route.Collection put(String path1, String path2,
    * @param filter A filter to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Collection put(String path1, String path2, Route.Filter filter);
 
   /**
@@ -1044,6 +1099,7 @@ Route.Collection put(String path1, String path2,
    * @param filter A filter to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Collection put(String path1, String path2, String path3, Route.Filter filter);
 
   /**
@@ -1059,6 +1115,7 @@ Route.Collection put(String path1, String path2,
    * @param handler A route to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Definition patch(String path, Route.Handler handler);
 
   /**
@@ -1075,6 +1132,7 @@ Route.Collection put(String path1, String path2,
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Collection patch(String path1, String path2, Route.Handler handler);
 
   /**
@@ -1109,6 +1167,7 @@ Route.Collection put(String path1, String path2,
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Definition patch(String path, Route.OneArgHandler handler);
 
   /**
@@ -1127,6 +1186,7 @@ Route.Collection put(String path1, String path2,
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Collection patch(String path1, String path2, Route.OneArgHandler handler);
 
   /**
@@ -1146,6 +1206,7 @@ Route.Collection put(String path1, String path2,
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Collection patch(String path1, String path2, String path3, Route.OneArgHandler handler);
 
   /**
@@ -1163,6 +1224,7 @@ Route.Collection put(String path1, String path2,
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Definition patch(String path, Route.ZeroArgHandler handler);
 
   /**
@@ -1181,6 +1243,7 @@ Route.Collection put(String path1, String path2,
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Collection patch(String path1, String path2, Route.ZeroArgHandler handler);
 
   /**
@@ -1200,6 +1263,7 @@ Route.Collection put(String path1, String path2,
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Collection patch(String path1, String path2, String path3, Route.ZeroArgHandler handler);
 
   /**
@@ -1215,6 +1279,7 @@ Route.Collection put(String path1, String path2,
    * @param filter A callback to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Definition patch(String path, Route.Filter filter);
 
   /**
@@ -1231,6 +1296,7 @@ Route.Collection put(String path1, String path2,
    * @param filter A filter to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Collection patch(String path1, String path2, Route.Filter filter);
 
   /**
@@ -1248,6 +1314,7 @@ Route.Collection put(String path1, String path2,
    * @param filter A filter to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Collection patch(String path1, String path2, String path3, Route.Filter filter);
 
   /**
@@ -1265,6 +1332,7 @@ Route.Collection put(String path1, String path2,
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Definition delete(String path, Route.Handler handler);
 
   /**
@@ -1283,6 +1351,7 @@ Route.Collection put(String path1, String path2,
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Collection delete(String path1, String path2, Route.Handler handler);
 
   /**
@@ -1302,6 +1371,7 @@ Route.Collection put(String path1, String path2,
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Collection delete(String path1, String path2, String path3, Route.Handler handler);
 
   /**
@@ -1319,6 +1389,7 @@ Route.Collection put(String path1, String path2,
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Definition delete(String path, Route.OneArgHandler handler);
 
   /**
@@ -1337,6 +1408,7 @@ Route.Collection put(String path1, String path2,
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Collection delete(String path1, String path2, Route.OneArgHandler handler);
 
   /**
@@ -1356,6 +1428,7 @@ Route.Collection put(String path1, String path2,
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Collection delete(String path1, String path2, String path3, Route.OneArgHandler handler);
 
   /**
@@ -1373,6 +1446,7 @@ Route.Collection put(String path1, String path2,
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Definition delete(String path, Route.ZeroArgHandler handler);
 
   /**
@@ -1389,6 +1463,7 @@ Route.Collection put(String path1, String path2,
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Collection delete(String path1, String path2, Route.ZeroArgHandler handler);
 
   /**
@@ -1406,6 +1481,7 @@ Route.Collection put(String path1, String path2,
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Collection delete(String path1, String path2, String path3, Route.ZeroArgHandler handler);
 
   /**
@@ -1422,6 +1498,7 @@ Route.Collection put(String path1, String path2,
    * @param filter A callback to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Definition delete(String path, Route.Filter filter);
 
   /**
@@ -1439,6 +1516,7 @@ Route.Collection put(String path1, String path2,
    * @param filter A filter to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Collection delete(String path1, String path2, Route.Filter filter);
 
   /**
@@ -1457,6 +1535,7 @@ Route.Collection put(String path1, String path2,
    * @param filter A filter to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Collection delete(String path1,
       String path2, String path3,
       Route.Filter filter);
@@ -1474,6 +1553,7 @@ Route.Collection delete(String path1,
    * @param handler A callback to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Definition trace(String path, Route.Handler handler);
 
   /**
@@ -1489,6 +1569,7 @@ Route.Collection delete(String path1,
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Definition trace(String path, Route.OneArgHandler handler);
 
   /**
@@ -1504,6 +1585,7 @@ Route.Collection delete(String path1,
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Definition trace(String path, Route.ZeroArgHandler handler);
 
   /**
@@ -1519,6 +1601,7 @@ Route.Collection delete(String path1,
    * @param filter A callback to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Definition trace(String path, Route.Filter filter);
 
   /**
@@ -1533,6 +1616,7 @@ Route.Collection delete(String path1,
    *
    * @return A new route definition.
    */
+  @Nonnull
   Route.Definition trace();
 
   /**
@@ -1547,6 +1631,7 @@ Route.Collection delete(String path1,
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Definition connect(String path, Route.Handler handler);
 
   /**
@@ -1562,6 +1647,7 @@ Route.Collection delete(String path1,
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Definition connect(String path, Route.OneArgHandler handler);
 
   /**
@@ -1577,6 +1663,7 @@ Route.Collection delete(String path1,
    * @param handler A handler to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Definition connect(String path, Route.ZeroArgHandler handler);
 
   /**
@@ -1592,6 +1679,7 @@ Route.Collection delete(String path1,
    * @param filter A filter to execute.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Definition connect(String path, Route.Filter filter);
 
   /**
@@ -1621,6 +1709,7 @@ Route.Collection delete(String path1,
    * @param path The path to publish.
    * @return A new route definition.
    */
+  @Nonnull
   default Route.Definition assets(final String path) {
     return assets(path, "/");
   }
@@ -1654,6 +1743,7 @@ default Route.Definition assets(final String path) {
    * @param basedir Base directory.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Definition assets(final String path, Path basedir);
 
   /**
@@ -1699,6 +1789,7 @@ default Route.Definition assets(final String path) {
    * @param location A resource location.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Definition assets(String path, String location);
 
   /**
@@ -1709,6 +1800,7 @@ default Route.Definition assets(final String path) {
    * @param handler Asset handler.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Definition assets(String path, AssetHandler handler);
 
   /**
@@ -1745,6 +1837,7 @@ default Route.Definition assets(final String path) {
    * @param routeClass A route(s) class.
    * @return This jooby instance.
    */
+  @Nonnull
   Route.Collection use(Class<?> routeClass);
 
   /**
@@ -1802,6 +1895,7 @@ default Route.Definition assets(final String path) {
    * @param chain Chain of before handler.
    * @return A new route definition.
    */
+  @Nonnull
   default Route.Collection before(final Route.Before handler, final Route.Before... chain) {
     return before("*", handler, chain);
   }
@@ -1861,6 +1955,7 @@ default Route.Collection before(final Route.Before handler, final Route.Before..
    * @param chain Chain of before handler.
    * @return A new route definition.
    */
+  @Nonnull
   default Route.Collection before(final String pattern, final Route.Before handler,
       final Route.Before... chain) {
     return before("*", pattern, handler, chain);
@@ -1922,6 +2017,7 @@ default Route.Collection before(final String pattern, final Route.Before handler
    * @param chain Chain of before handler.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Collection before(String method, String pattern, Route.Before handler,
       Route.Before... chain);
 
@@ -1988,6 +2084,7 @@ Route.Collection before(String method, String pattern, Route.Before handler,
    * @param chain After chain.
    * @return A new route definition.
    */
+  @Nonnull
   default Route.Collection after(final Route.After handler, final Route.After... chain) {
     return after("*", handler, chain);
   }
@@ -2054,6 +2151,7 @@ default Route.Collection after(final Route.After handler, final Route.After... c
    * @param chain After chain.
    * @return A new route definition.
    */
+  @Nonnull
   default Route.Collection after(final String pattern, final Route.After handler,
       final Route.After... chain) {
     return after("*", pattern, handler, chain);
@@ -2123,6 +2221,7 @@ default Route.Collection after(final String pattern, final Route.After handler,
    * @param chain After chain.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Collection after(String method, String pattern, Route.After handler, Route.After... chain);
 
   /**
@@ -2228,6 +2327,7 @@ default Route.Collection after(final String pattern, final Route.After handler,
    * @param chain Complete chain.
    * @return A new route definition.
    */
+  @Nonnull
   default Route.Collection complete(final Route.Complete handler, final Route.Complete... chain) {
     return complete("*", handler, chain);
   }
@@ -2336,6 +2436,7 @@ default Route.Collection complete(final Route.Complete handler, final Route.Comp
    * @param chain Complete chain.
    * @return A new route definition.
    */
+  @Nonnull
   default Route.Collection complete(final String pattern, final Route.Complete handler,
       final Route.Complete... chain) {
     return complete("*", pattern, handler, chain);
@@ -2445,6 +2546,7 @@ default Route.Collection complete(final String pattern, final Route.Complete han
    * @param chain Complete chain.
    * @return A new route definition.
    */
+  @Nonnull
   Route.Collection complete(String method, String pattern, Route.Complete handler,
       Route.Complete... chain);
 
@@ -2465,6 +2567,7 @@ Route.Collection complete(String method, String pattern, Route.Complete handler,
    * @param handler A connect callback.
    * @return A new WebSocket definition.
    */
+  @Nonnull
   default WebSocket.Definition ws(final String path, final WebSocket.OnOpen1 handler) {
     return ws(path, (WebSocket.OnOpen) handler);
   }
@@ -2486,12 +2589,36 @@ default WebSocket.Definition ws(final String path, final WebSocket.OnOpen1 handl
    * @param handler A connect callback.
    * @return A new WebSocket definition.
    */
+  @Nonnull
   WebSocket.Definition ws(String path, WebSocket.OnOpen handler);
 
+  /**
+   * Append a new WebSocket handler under the given path.
+   *
+   * <pre>
+   *   ws(MyHandler.class);
+   * </pre>
+   *
+   *  @param handler A message callback.
+   * @return A new WebSocket definition.
+   */
+  @Nonnull
   default <T> WebSocket.Definition ws(final Class<? extends WebSocket.OnMessage<T>> handler) {
     return ws("", handler);
   }
 
+  /**
+   * Append a new WebSocket handler under the given path.
+   *
+   * <pre>
+   *   ws("/ws", MyHandler.class);
+   * </pre>
+   *
+   * @param path A path pattern.
+   * @param handler A message callback.
+   * @return A new WebSocket definition.
+   */
+  @Nonnull
   <T> WebSocket.Definition ws(String path, Class<? extends WebSocket.OnMessage<T>> handler);
 
   /**
@@ -2510,6 +2637,7 @@ default <T> WebSocket.Definition ws(final Class<? extends WebSocket.OnMessage<T>
    * @param handler Callback. It might executed in a different thread (web server choice).
    * @return A route definition.
    */
+  @Nonnull
   Route.Definition sse(String path, Sse.Handler handler);
 
   /**
@@ -2528,6 +2656,7 @@ default <T> WebSocket.Definition ws(final Class<? extends WebSocket.OnMessage<T>
    * @param handler Callback. It might executed in a different thread (web server choice).
    * @return A route definition.
    */
+  @Nonnull
   Route.Definition sse(String path, Sse.Handler1 handler);
 
   /**
@@ -2554,6 +2683,7 @@ default <T> WebSocket.Definition ws(final Class<? extends WebSocket.OnMessage<T>
    * @param callback Route callback.
    * @return A route collection.
    */
+  @Nonnull
   Route.Collection with(Runnable callback);
 
   /**
@@ -2574,6 +2704,7 @@ default <T> WebSocket.Definition ws(final Class<? extends WebSocket.OnMessage<T>
    * @param mapper Route mapper to append.
    * @return This instance.
    */
+  @Nonnull
   Router map(final Mapper<?> mapper);
 
   /**
@@ -2610,6 +2741,7 @@ default <T> WebSocket.Definition ws(final Class<? extends WebSocket.OnMessage<T>
    * @param err A route error handler.
    * @return This jooby instance.
    */
+  @Nonnull
   Router err(Err.Handler err);
 
   /**
@@ -2621,6 +2753,7 @@ default <T> WebSocket.Definition ws(final Class<? extends WebSocket.OnMessage<T>
    * @param handler A route error handler.
    * @return This jooby instance.
    */
+  @Nonnull
   default Router err(final Class<? extends Throwable> type, final Err.Handler handler) {
     return err((req, rsp, x) -> {
       if (type.isInstance(x) || type.isInstance(x.getCause())) {
@@ -2637,6 +2770,7 @@ default Router err(final Class<? extends Throwable> type, final Err.Handler hand
    * @param handler A route error handler.
    * @return This jooby instance.
    */
+  @Nonnull
   default Router err(final int statusCode, final Err.Handler handler) {
     return err((req, rsp, x) -> {
       if (statusCode == x.statusCode()) {
@@ -2653,6 +2787,7 @@ default Router err(final int statusCode, final Err.Handler handler) {
    * @param handler A route error handler.
    * @return This jooby instance.
    */
+  @Nonnull
   default Router err(final Status code, final Err.Handler handler) {
     return err((req, rsp, x) -> {
       if (code.value() == x.statusCode()) {
@@ -2669,6 +2804,7 @@ default Router err(final Status code, final Err.Handler handler) {
    * @param handler A route error handler.
    * @return This jooby instance.
    */
+  @Nonnull
   default Router err(final Predicate<Status> predicate, final Err.Handler handler) {
     return err((req, rsp, err) -> {
       if (predicate.test(Status.valueOf(err.statusCode()))) {
@@ -2735,6 +2871,7 @@ default Router err(final Predicate<Status> predicate, final Err.Handler handler)
    * @return A new deferred handler.
    * @see Deferred
    */
+  @Nonnull
   Route.OneArgHandler promise(Deferred.Initializer initializer);
 
   /**
@@ -2768,6 +2905,7 @@ default Router err(final Predicate<Status> predicate, final Err.Handler handler)
    * @return A new deferred handler.
    * @see Deferred
    */
+  @Nonnull
   Route.OneArgHandler promise(String executor, Deferred.Initializer initializer);
 
   /**
@@ -2796,6 +2934,7 @@ default Router err(final Predicate<Status> predicate, final Err.Handler handler)
    * @return A new deferred handler.
    * @see Deferred
    */
+  @Nonnull
   Route.OneArgHandler promise(Deferred.Initializer0 initializer);
 
   /**
@@ -2819,6 +2958,7 @@ default Router err(final Predicate<Status> predicate, final Err.Handler handler)
    * @return A new deferred handler.
    * @see Deferred
    */
+  @Nonnull
   Route.OneArgHandler promise(String executor, Deferred.Initializer0 initializer);
 
   /**
@@ -2842,6 +2982,7 @@ default Router err(final Predicate<Status> predicate, final Err.Handler handler)
    * @param handler Application block.
    * @return A new deferred handler.
    */
+  @Nonnull
   default Route.ZeroArgHandler deferred(final String executor, final Route.OneArgHandler handler) {
     return () -> Deferred.deferred(executor, handler);
   }
@@ -2877,6 +3018,7 @@ default Route.ZeroArgHandler deferred(final String executor, final Route.OneArgH
    * @param handler Application block.
    * @return A new deferred handler.
    */
+  @Nonnull
   default Route.ZeroArgHandler deferred(final Route.OneArgHandler handler) {
     return () -> Deferred.deferred(handler);
   }
@@ -2902,6 +3044,7 @@ default Route.ZeroArgHandler deferred(final Route.OneArgHandler handler) {
    * @param handler Application block.
    * @return A new deferred handler.
    */
+  @Nonnull
   default Route.ZeroArgHandler deferred(final String executor, final Route.ZeroArgHandler handler) {
     return () -> Deferred.deferred(executor, handler);
   }
@@ -2937,6 +3080,7 @@ default Route.ZeroArgHandler deferred(final String executor, final Route.ZeroArg
    * @param handler Application block.
    * @return A new deferred handler.
    */
+  @Nonnull
   default Route.ZeroArgHandler deferred(final Route.ZeroArgHandler handler) {
     return () -> Deferred.deferred(handler);
   }
diff --git a/jooby/src/main/java/org/jooby/Session.java b/jooby/src/main/java/org/jooby/Session.java
index 030df892af..3bd994c036 100644
--- a/jooby/src/main/java/org/jooby/Session.java
+++ b/jooby/src/main/java/org/jooby/Session.java
@@ -213,6 +213,8 @@
 
 import com.google.common.io.BaseEncoding;
 
+import javax.annotation.Nonnull;
+
 /**
  * <p>
  * Sessions are created on demand via: {@link Request#session()}.
@@ -525,6 +527,7 @@ interface Builder {
    *
    * @return Session ID.
    */
+  @Nonnull
   String id();
 
   /**
@@ -574,11 +577,13 @@ interface Builder {
    * @param name Attribute's name.
    * @return Value as mutant.
    */
+  @Nonnull
   Mutant get(final String name);
 
   /**
    * @return An immutable copy of local attributes.
    */
+  @Nonnull
   Map<String, String> attributes();
 
   /**
@@ -597,6 +602,7 @@ interface Builder {
    * @param value Attribute's value.
    * @return This session.
    */
+  @Nonnull
   default Session set(final String name, final byte value) {
     return set(name, Byte.toString(value));
   }
@@ -609,6 +615,7 @@ default Session set(final String name, final byte value) {
    * @param value Attribute's value.
    * @return This session.
    */
+  @Nonnull
   default Session set(final String name, final char value) {
     return set(name, Character.toString(value));
   }
@@ -621,6 +628,7 @@ default Session set(final String name, final char value) {
    * @param value Attribute's value.
    * @return This session.
    */
+  @Nonnull
   default Session set(final String name, final boolean value) {
     return set(name, Boolean.toString(value));
   }
@@ -633,6 +641,7 @@ default Session set(final String name, final boolean value) {
    * @param value Attribute's value.
    * @return This session.
    */
+  @Nonnull
   default Session set(final String name, final short value) {
     return set(name, Short.toString(value));
   }
@@ -645,6 +654,7 @@ default Session set(final String name, final short value) {
    * @param value Attribute's value.
    * @return This session.
    */
+  @Nonnull
   default Session set(final String name, final int value) {
     return set(name, Integer.toString(value));
   }
@@ -657,6 +667,7 @@ default Session set(final String name, final int value) {
    * @param value Attribute's value.
    * @return This session.
    */
+  @Nonnull
   default Session set(final String name, final long value) {
     return set(name, Long.toString(value));
   }
@@ -669,6 +680,7 @@ default Session set(final String name, final long value) {
    * @param value Attribute's value.
    * @return This session.
    */
+  @Nonnull
   default Session set(final String name, final float value) {
     return set(name, Float.toString(value));
   }
@@ -681,6 +693,7 @@ default Session set(final String name, final float value) {
    * @param value Attribute's value.
    * @return This session.
    */
+  @Nonnull
   default Session set(final String name, final double value) {
     return set(name, Double.toString(value));
   }
@@ -693,6 +706,7 @@ default Session set(final String name, final double value) {
    * @param value Attribute's value.
    * @return This session.
    */
+  @Nonnull
   default Session set(final String name, final CharSequence value) {
     return set(name, value.toString());
   }
@@ -705,6 +719,7 @@ default Session set(final String name, final CharSequence value) {
    * @param value Attribute's value.
    * @return This session.
    */
+  @Nonnull
   Session set(final String name, final String value);
 
   /**
@@ -713,6 +728,7 @@ default Session set(final String name, final CharSequence value) {
    * @param name Attribute's name.
    * @return Existing value or empty optional.
    */
+  @Nonnull
   Mutant unset(final String name);
 
   /**
@@ -720,6 +736,7 @@ default Session set(final String name, final CharSequence value) {
    *
    * @return This session.
    */
+  @Nonnull
   Session unset();
 
   /**
diff --git a/jooby/src/main/java/org/jooby/Sse.java b/jooby/src/main/java/org/jooby/Sse.java
index a939ac80c9..783f502f17 100644
--- a/jooby/src/main/java/org/jooby/Sse.java
+++ b/jooby/src/main/java/org/jooby/Sse.java
@@ -216,6 +216,7 @@
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+import javax.annotation.Nonnull;
 import java.io.IOException;
 import java.nio.channels.ClosedChannelException;
 import java.nio.charset.StandardCharsets;
@@ -737,6 +738,7 @@ protected void handshake(final Request req, final Runnable handler) throws Excep
    *
    * @return Sse unique ID (like a session ID).
    */
+  @Nonnull
   public String id() {
     return id;
   }
@@ -746,6 +748,7 @@ public String id() {
    *
    * @return Last event id.
    */
+  @Nonnull
   public Optional<String> lastEventId() {
     return lastEventId(String.class);
   }
@@ -757,6 +760,7 @@ public Optional<String> lastEventId() {
    * @param <T> Event id type.
    * @return Last event id.
    */
+  @Nonnull
   public <T> Optional<T> lastEventId(final Class<T> type) {
     return lastEventId.toOptional(type);
   }
@@ -768,6 +772,7 @@ public <T> Optional<T> lastEventId(final Class<T> type) {
    * @param task Task to run.
    * @return This instance.
    */
+  @Nonnull
   public Sse onClose(final Throwing.Runnable task) {
     onclose.set(task);
     return this;
@@ -797,6 +802,7 @@ public Sse onClose(final Throwing.Runnable task) {
    * @param type Media type, like: json, xml.
    * @return A future. The success callback contains the {@link Event#id()}.
    */
+  @Nonnull
   public CompletableFuture<Optional<Object>> send(final Object data, final String type) {
     return send(data, MediaType.valueOf(type));
   }
@@ -824,6 +830,7 @@ public CompletableFuture<Optional<Object>> send(final Object data, final String
    * @param type Media type, like: json, xml.
    * @return A future. The success callback contains the {@link Event#id()}.
    */
+  @Nonnull
   public CompletableFuture<Optional<Object>> send(final Object data, final MediaType type) {
     return event(data).type(type).send();
   }
@@ -850,6 +857,7 @@ public CompletableFuture<Optional<Object>> send(final Object data, final MediaTy
    * @param data Event data.
    * @return A future. The success callback contains the {@link Event#id()}.
    */
+  @Nonnull
   public CompletableFuture<Optional<Object>> send(final Object data) {
     return event(data).send();
   }
@@ -883,6 +891,7 @@ public CompletableFuture<Optional<Object>> send(final Object data) {
    * @param data Event data.
    * @return A new event.
    */
+  @Nonnull
   public Event event(final Object data) {
     return new Event(this, data);
   }
@@ -894,6 +903,7 @@ public Event event(final Object data) {
    * @param <T> Service type.
    * @return A ready to use object.
    */
+  @Nonnull
   public <T> T require(final Class<T> type) {
     return require(Key.get(type));
   }
@@ -906,6 +916,7 @@ public <T> T require(final Class<T> type) {
    * @param <T> Service type.
    * @return A ready to use object.
    */
+  @Nonnull
   public <T> T require(final String name, final Class<T> type) {
     return require(Key.get(type, Names.named(name)));
   }
@@ -917,6 +928,7 @@ public <T> T require(final String name, final Class<T> type) {
    * @param <T> Service type.
    * @return A ready to use object.
    */
+  @Nonnull
   public <T> T require(final TypeLiteral<T> type) {
     return require(Key.get(type));
   }
@@ -928,6 +940,7 @@ public <T> T require(final TypeLiteral<T> type) {
    * @param <T> Service type.
    * @return A ready to use object.
    */
+  @Nonnull
   public <T> T require(final Key<T> key) {
     return injector.getInstance(key);
   }
@@ -960,6 +973,7 @@ public <T> T require(final Key<T> key) {
    * @param unit Time unit.
    * @return This instance.
    */
+  @Nonnull
   public Sse keepAlive(final int time, final TimeUnit unit) {
     return keepAlive(unit.toMillis(time));
   }
@@ -991,6 +1005,7 @@ public Sse keepAlive(final int time, final TimeUnit unit) {
    * @param millis Keep alive time in millis.
    * @return This instance.
    */
+  @Nonnull
   public Sse keepAlive(final long millis) {
     scheduler.schedule(new KeepAlive(this, millis), millis, TimeUnit.MILLISECONDS);
     return this;
diff --git a/jooby/src/main/java/org/jooby/Upload.java b/jooby/src/main/java/org/jooby/Upload.java
index 7193493bcc..376d83fe2d 100644
--- a/jooby/src/main/java/org/jooby/Upload.java
+++ b/jooby/src/main/java/org/jooby/Upload.java
@@ -203,6 +203,7 @@
  */
 package org.jooby;
 
+import javax.annotation.Nonnull;
 import java.io.Closeable;
 import java.io.File;
 import java.io.IOException;
@@ -218,11 +219,13 @@ public interface Upload extends Closeable {
   /**
    * @return File's name.
    */
+  @Nonnull
   String name();
 
   /**
    * @return File media type.
    */
+  @Nonnull
   MediaType type();
 
   /**
@@ -231,6 +234,7 @@ public interface Upload extends Closeable {
    * @param name Header's name.
    * @return A header value.
    */
+  @Nonnull
   Mutant header(String name);
 
   /**
@@ -239,6 +243,7 @@ public interface Upload extends Closeable {
    * @return A temp file.
    * @throws IOException If file doesn't exist.
    */
+  @Nonnull
   File file() throws IOException;
 
 }
diff --git a/jooby/src/main/java/org/jooby/View.java b/jooby/src/main/java/org/jooby/View.java
index 0450bfdcb8..7bfa181dc8 100644
--- a/jooby/src/main/java/org/jooby/View.java
+++ b/jooby/src/main/java/org/jooby/View.java
@@ -205,6 +205,7 @@
 
 import static java.util.Objects.requireNonNull;
 
+import javax.annotation.Nonnull;
 import java.io.FileNotFoundException;
 import java.util.HashMap;
 import java.util.Map;
@@ -273,6 +274,7 @@ protected View(final String name) {
   /**
    * @return View's name.
    */
+  @Nonnull
   public String name() {
     return name;
   }
@@ -284,6 +286,7 @@ public String name() {
    * @param value Attribute's value.
    * @return This view.
    */
+  @Nonnull
   public View put(final String name, final Object value) {
     requireNonNull(name, "Model name is required.");
     model.put(name, value);
@@ -296,6 +299,7 @@ public View put(final String name, final Object value) {
    * @param values Attribute's value.
    * @return This view.
    */
+  @Nonnull
   public View put(final Map<String, ?> values) {
     values.forEach((k, v) -> model.put(k, v));
     return this;
@@ -304,11 +308,14 @@ public View put(final Map<String, ?> values) {
   /**
    * @return View's model.
    */
+
+  @Nonnull
   public Map<String, ?> model() {
     return model;
   }
 
   @Override
+  @Nonnull
   public Result set(final Object content) {
     throw new UnsupportedOperationException("Not allowed in views, use one of the put methods.");
   }
diff --git a/jooby/src/main/java/org/jooby/WebSocket.java b/jooby/src/main/java/org/jooby/WebSocket.java
index 18091f48b0..4da880ed57 100644
--- a/jooby/src/main/java/org/jooby/WebSocket.java
+++ b/jooby/src/main/java/org/jooby/WebSocket.java
@@ -219,6 +219,8 @@
 import com.google.inject.Key;
 import com.google.inject.TypeLiteral;
 
+import javax.annotation.Nonnull;
+
 /**
  * <h1>WebSockets</h1>
  * <p>
@@ -766,26 +768,31 @@ interface Handler<T> extends OnClose, OnMessage<T>, OnError, OnOpen {
   /**
    * @return Current request path.
    */
+  @Nonnull
   String path();
 
   /**
    * @return The currently matched pattern.
    */
+  @Nonnull
   String pattern();
 
   /**
    * @return The currently matched path variables (if any).
    */
+  @Nonnull
   Map<Object, String> vars();
 
   /**
    * @return The type this route can consumes, defaults is: {@code * / *}.
    */
+  @Nonnull
   MediaType consumes();
 
   /**
    * @return The type this route can produces, defaults is: {@code * / *}.
    */
+  @Nonnull
   MediaType produces();
 
   /**
@@ -968,7 +975,5 @@ default void broadcast(final Object data, final OnError err) throws Exception {
    * @param err An err callback.
    * @throws Exception If something goes wrong.
    */
-  void broadcast(Object data, SuccessCallback success, OnError err)
-      throws Exception;
-
+  void broadcast(Object data, SuccessCallback success, OnError err) throws Exception;
 }
diff --git a/jooby/src/main/java/org/jooby/package-info.java b/jooby/src/main/java/org/jooby/package-info.java
new file mode 100644
index 0000000000..3b3b847d37
--- /dev/null
+++ b/jooby/src/main/java/org/jooby/package-info.java
@@ -0,0 +1,8 @@
+/**
+ * <h1>do more, more easily</h1>
+ * <p>
+ *   Jooby a scalable, fast and modular micro web framework for Java and Kotlin.
+ * </p>
+ */
+@javax.annotation.ParametersAreNonnullByDefault
+package org.jooby;
diff --git a/pom.xml b/pom.xml
index bbe26576a9..d5220e14eb 100644
--- a/pom.xml
+++ b/pom.xml
@@ -1474,6 +1474,13 @@
         <version>${maven-antrun-plugin.version}</version>
       </dependency>
 
+      <!-- jsr350-->
+      <dependency>
+        <groupId>com.google.code.findbugs</groupId>
+        <artifactId>jsr305</artifactId>
+        <version>${jsr305.version}</version>
+      </dependency>
+
       <!-- sitemap -->
       <dependency>
         <groupId>cz.jiripinkas</groupId>
@@ -3007,7 +3014,7 @@ org.eclipse.jdt.apt.processorOptions/defaultOverwrite=true
     <hikariCP.version>2.6.1</hikariCP.version>
     <hibernate.version>5.2.1.Final</hibernate.version>
     <hibernate4.version>4.3.9.Final</hibernate4.version>
-    <jsr305.version>3.0.0</jsr305.version>
+    <jsr305.version>3.0.2</jsr305.version>
     <http-client.version>4.5.2</http-client.version>
     <rest-assured.version>3.0.1</rest-assured.version>
     <async-http-client.version>1.9.36</async-http-client.version>