diff --git a/pylspclient/lsp_endpoint.py b/pylspclient/lsp_endpoint.py
index 7de605a..b811b3a 100644
--- a/pylspclient/lsp_endpoint.py
+++ b/pylspclient/lsp_endpoint.py
@@ -1,12 +1,20 @@
 from __future__ import print_function
 import threading
+import collections
+from pylspclient import lsp_structs
+
+
+class MethodNotFound(object):
+    def __call__(self, jsonrpc_message):
+        raise lsp_structs.ResponseError("Method not found: {method}".format(method=jsonrpc_message["method"]), lsp_structs.ErrorCodes.MethodNotFound)
+
 
 class LspEndpoint(threading.Thread):
-    def __init__(self, json_rpc_endpoint, default_callback=print, callbacks={}):
+    def __init__(self, json_rpc_endpoint, default_method_callback=MethodNotFound(), method_callbacks={}, default_notify_callback=print, notify_callbacks={}):
         threading.Thread.__init__(self)
         self.json_rpc_endpoint = json_rpc_endpoint
-        self.callbacks = callbacks
-        self.default_callback = default_callback
+        self.notify_callbacks = collections.defaultdict(lambda : default_notify_callback, notify_callbacks)
+        self.method_callbacks = collections.defaultdict(lambda : default_method_callback, method_callbacks)
         self.event_dict = {}
         self.response_dict = {}
         self.next_id = 0
@@ -36,14 +44,31 @@ class LspEndpoint(threading.Thread):
             if "result" in jsonrpc_message or "error" in jsonrpc_message:
                 self.handle_result(jsonrpc_message)
             elif "method" in jsonrpc_message:
-                if jsonrpc_message["method"] in self.callbacks:
-                    self.callbacks[jsonrpc_message["method"]](jsonrpc_message)
+                if "id" in jsonrpc_message:
+                    # a call for method
+                    try:
+                        result = self.method_callbacks[jsonrpc_message["method"]](jsonrpc_message)
+                        self.send_response(jsonrpc_message["id"], result, None)
+                    except lsp_structs.ResponseError as e:
+                        self.send_response(jsonrpc_message["id"], None, e)                         
                 else:
-                    self.default_callback(jsonrpc_message)
+                    # a call for notify
+                    self.notify_callbacks[jsonrpc_message["method"]](jsonrpc_message)
             else:
                 print("unknown jsonrpc message")
-    
-    
+   
+
+    def send_response(self, id, result, error):
+        message_dict = {}
+        message_dict["jsonrpc"] = "2.0"
+        message_dict["id"] = id
+        if result:
+            message_dict["result"] = result
+        if error:
+            message_dict["error"] = error
+        self.json_rpc_endpoint.send_request(message_dict)
+   
+
     def send_message(self, method_name, params, id = None):
         message_dict = {}
         message_dict["jsonrpc"] = "2.0"
@@ -63,8 +88,10 @@ class LspEndpoint(threading.Thread):
         self.send_message(method_name, kwargs, current_id)
         cond.wait()
         cond.release()
-        # TODO: check if error, and throw an exception
         response = self.response_dict[current_id]
+        if "error" in response:
+            error = response["error"]
+            raise lsp_structs.ResponseError(error.get("code"), error.get("message"), error.get("data"))
         return response["result"]
 
 
diff --git a/pylspclient/lsp_structs.py b/pylspclient/lsp_structs.py
index 6c8e938..04ebaa3 100644
--- a/pylspclient/lsp_structs.py
+++ b/pylspclient/lsp_structs.py
@@ -425,3 +425,26 @@ class CompletionList(object):
         """
         self.isIncomplete = isIncomplete
         self.items = [to_type(i, CompletionItem) for i in items]
+
+class ErrorCodes(object):
+	# Defined by JSON RPC
+	ParseError = -32700
+	InvalidRequest = -32600
+	MethodNotFound = -32601
+	InvalidParams = -32602
+	InternalError = -32603
+	serverErrorStart = -32099
+	serverErrorEnd = -32000
+	ServerNotInitialized = -32002
+	UnknownErrorCode = -32001
+
+	# Defined by the protocol.
+	RequestCancelled = -32800
+	ContentModified = -32801
+
+class ResponseError(Exception):
+    def __init__(self, code, message, data = None):
+        self.code = code
+        self.message = message
+        if data:
+            self.data = data
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