diff --git a/pycorenlp/__init__.py b/pycorenlp/__init__.py
index b031cf7..8d7744b 100644
--- a/pycorenlp/__init__.py
+++ b/pycorenlp/__init__.py
@@ -1 +1 @@
-from pycorenlp.corenlp import StanfordCoreNLP
+from pycorenlp.corenlp import StanfordCoreNLP, StanfordCoreNLPError, NoStanfordCoreNLPServer
diff --git a/pycorenlp/corenlp.py b/pycorenlp/corenlp.py
index 6eb2175..51147f3 100644
--- a/pycorenlp/corenlp.py
+++ b/pycorenlp/corenlp.py
@@ -1,7 +1,24 @@
 import json, requests
 
-class StanfordCoreNLP:
+class NoStanfordCoreNLPServer(Exception):
+    def __init__(self, server_url):
+        self.server_url = server_url
+
+    def __str__(self):
+        return ('Cannot connect to <%s>.\nPlease start the CoreNLP server, e.g.:\n'
+                '$ cd stanford-corenlp-full-2015-12-09/\n'
+                '$ java -mx4g -cp "*" edu.stanford.nlp.pipeline.StanfordCoreNLPServer'
+                % (self.server_url))
 
+class StanfordCoreNLPError(Exception):
+    def __init__(self, reason, message):
+        self.reason = reason
+        self.message = message
+
+    def __str__(self):
+        return "%s(%s): %s" % (self.__class__.__name__,self.reason,self.message)
+
+class StanfordCoreNLP:
     def __init__(self, server_url):
         if server_url[-1] == '/':
             server_url = server_url[:-1]
@@ -18,23 +35,17 @@ def annotate(self, text, properties=None):
         try:
             requests.get(self.server_url)
         except requests.exceptions.ConnectionError:
-            raise Exception('Check whether you have started the CoreNLP server e.g.\n'
-            '$ cd stanford-corenlp-full-2015-12-09/ \n'
-            '$ java -mx4g -cp "*" edu.stanford.nlp.pipeline.StanfordCoreNLPServer')
+            raise NoStanfordCoreNLPServer(self.server_url)
 
-        data = text.encode()
         r = requests.post(
             self.server_url, params={
                 'properties': str(properties)
-            }, data=data, headers={'Connection': 'close'})
-        output = r.text
-        if ('outputFormat' in properties
-             and properties['outputFormat'] == 'json'):
-            try:
-                output = json.loads(output, encoding='utf-8', strict=True)
-            except:
-                pass
-        return output
+            }, data=text.encode(), headers={'Connection': 'close'})
+        if not r.ok:
+            raise StanfordCoreNLPError(r.reason, r.text)
+        if properties.get('outputFormat') == 'json':
+            return json.loads(r.text)
+        return r.text
 
     def tokensregex(self, text, pattern, filter):
         return self.regex('/tokensregex', text, pattern, filter)
@@ -48,9 +59,6 @@ def regex(self, endpoint, text, pattern, filter):
                 'pattern':  pattern,
                 'filter': filter
             }, data=text)
-        output = r.text
-        try:
-            output = json.loads(r.text)
-        except:
-            pass
-        return output
+        if not r.ok:
+            raise StanfordCoreNLPError(r.reason, r.text)
+        return json.loads(r.text)