diff --git a/src/tools/build-manifest/README.md b/src/tools/build-manifest/README.md
new file mode 100644
index 0000000000000..6834f56efe7db
--- /dev/null
+++ b/src/tools/build-manifest/README.md
@@ -0,0 +1,30 @@
+# build-manifest
+
+This tool generates the manifests uploaded to static.rust-lang.org and used by
+rustup. The tool is invoked by the bootstrap tool.
+
+## Testing changes locally
+
+In order to test the changes locally you need to have a valid dist directory
+available locally. If you don't want to build all the compiler, you can easily
+create one from the nightly artifacts with:
+
+```
+#!/bin/bash
+for cmpn in rust rustc rust-std rust-docs cargo; do
+    wget https://static.rust-lang.org/dist/${cmpn}-nightly-x86_64-unknown-linux-gnu.tar.gz
+done
+```
+
+Then, you can generate the manifest and all the packages from `path/to/dist` to
+`path/to/output` with:
+
+```
+$ BUILD_MANIFEST_DISABLE_SIGNING=1 cargo +nightly run \
+    path/to/dist path/to/output 1970-01-01 \
+    nightly nightly nightly nightly nightly nightly nightly \
+    http://example.com
+```
+
+In the future, if the tool complains about missing arguments just add more
+`nightly`s in the middle.
diff --git a/src/tools/build-manifest/src/main.rs b/src/tools/build-manifest/src/main.rs
index f43bd88d04f32..39d57f4c93b3c 100644
--- a/src/tools/build-manifest/src/main.rs
+++ b/src/tools/build-manifest/src/main.rs
@@ -121,6 +121,17 @@ static TARGETS: &'static [&'static str] = &[
     "x86_64-unknown-redox",
 ];
 
+static DOCS_TARGETS: &'static [&'static str] = &[
+    "i686-apple-darwin",
+    "i686-pc-windows-gnu",
+    "i686-pc-windows-msvc",
+    "i686-unknown-linux-gnu",
+    "x86_64-apple-darwin",
+    "x86_64-pc-windows-gnu",
+    "x86_64-pc-windows-msvc",
+    "x86_64-unknown-linux-gnu",
+];
+
 static MINGW: &'static [&'static str] = &[
     "i686-pc-windows-gnu",
     "x86_64-pc-windows-gnu",
@@ -216,9 +227,23 @@ struct Builder {
     rustfmt_git_commit_hash: Option<String>,
     llvm_tools_git_commit_hash: Option<String>,
     lldb_git_commit_hash: Option<String>,
+
+    should_sign: bool,
 }
 
 fn main() {
+    // Avoid signing packages while manually testing
+    // Do NOT set this envvar in CI
+    let should_sign = env::var("BUILD_MANIFEST_DISABLE_SIGNING").is_err();
+
+    // Safety check to ensure signing is always enabled on CI
+    // The CI environment variable is set by both Travis and AppVeyor
+    if !should_sign && env::var("CI").is_ok() {
+        println!("The 'BUILD_MANIFEST_DISABLE_SIGNING' env var can't be enabled on CI.");
+        println!("If you're not running this on CI, unset the 'CI' env var.");
+        panic!();
+    }
+
     let mut args = env::args().skip(1);
     let input = PathBuf::from(args.next().unwrap());
     let output = PathBuf::from(args.next().unwrap());
@@ -231,8 +256,12 @@ fn main() {
     let llvm_tools_release = args.next().unwrap();
     let lldb_release = args.next().unwrap();
     let s3_address = args.next().unwrap();
+
+    // Do not ask for a passphrase while manually testing
     let mut passphrase = String::new();
-    t!(io::stdin().read_to_string(&mut passphrase));
+    if should_sign {
+        t!(io::stdin().read_to_string(&mut passphrase));
+    }
 
     Builder {
         rust_release,
@@ -265,6 +294,8 @@ fn main() {
         rustfmt_git_commit_hash: None,
         llvm_tools_git_commit_hash: None,
         lldb_git_commit_hash: None,
+
+        should_sign,
     }.build();
 }
 
@@ -318,7 +349,7 @@ impl Builder {
         self.package("cargo", &mut manifest.pkg, HOSTS);
         self.package("rust-mingw", &mut manifest.pkg, MINGW);
         self.package("rust-std", &mut manifest.pkg, TARGETS);
-        self.package("rust-docs", &mut manifest.pkg, TARGETS);
+        self.package("rust-docs", &mut manifest.pkg, DOCS_TARGETS);
         self.package("rust-src", &mut manifest.pkg, &["*"]);
         self.package("rls-preview", &mut manifest.pkg, HOSTS);
         self.package("clippy-preview", &mut manifest.pkg, HOSTS);
@@ -402,11 +433,7 @@ impl Builder {
                         Some(p) => p,
                         None => return false,
                     };
-                    let target = match pkg.target.get(&c.target) {
-                        Some(t) => t,
-                        None => return false,
-                    };
-                    target.available
+                    pkg.target.get(&c.target).is_some()
                 };
                 extensions.retain(&has_component);
                 components.retain(&has_component);
@@ -588,6 +615,10 @@ impl Builder {
     }
 
     fn sign(&self, path: &Path) {
+        if !self.should_sign {
+            return;
+        }
+
         let filename = path.file_name().unwrap().to_str().unwrap();
         let asc = self.output.join(format!("{}.asc", filename));
         println!("signing: {:?}", path);