diff --git a/tests/unit/test_cassettes.py b/tests/unit/test_cassettes.py
index 413b154..3d358de 100644
--- a/tests/unit/test_cassettes.py
+++ b/tests/unit/test_cassettes.py
@@ -10,6 +10,7 @@ from vcr.compat import mock, contextlib
 from vcr.cassette import Cassette
 from vcr.errors import UnhandledHTTPRequestError
 from vcr.patch import force_reset
+from vcr.matchers import path, method, query, host
 from vcr.stubs import VCRHTTPSConnection
 
 
@@ -294,3 +295,18 @@ def test_use_as_decorator_on_generator():
         assert httplib.HTTPConnection is not original_http_connetion
         yield 2
     assert list(test_function()) == [1, 2]
+
+
+def test_similar_requests(tmpdir):
+    # WIP needs to be finished
+    @Cassette.use(inject=True, match_on=(path, query, host, method))
+    def test_function(cassette):
+        conn = httplib.HTTPConnection("www.python.org")
+        conn.request("GET", "/index.html?test=1")
+
+        conn = httplib.HTTPConnection("www.python.org")
+        conn.request("GET", "/index.html?test=0")
+
+        conn = httplib.HTTPConnection("www.cool.org")
+        conn.request("GET", "/index.html?test=0")
+        cassette.similar_requests()
diff --git a/vcr/cassette.py b/vcr/cassette.py
index db94224..79b62b6 100644
--- a/vcr/cassette.py
+++ b/vcr/cassette.py
@@ -1,6 +1,7 @@
-import sys
 import inspect
 import logging
+import operator
+import sys
 
 import wrapt
 
@@ -145,9 +146,33 @@ class CassetteContextDecorator(object):
         return new_args_getter
 
 
+class SimilarityScorer(object):
+
+    def __init__(self, matchers, request, ascending=False):
+        self._matchers = matchers
+        self._request = request
+        self._ascending = False
+
+    def score(self, candidate, play_count):
+        value = 1
+        total = 0
+        if play_count < 1:
+            total += value
+        if self._ascending:
+            value *= 2
+        for matcher in self._matchers[::-1]:
+            if matcher(self._request, candidate):
+                total += value
+            if self._ascending:
+                value *= 2
+        return total
+
+
 class Cassette(object):
     """A container for recorded requests and responses"""
 
+    max_playcount = 1
+
     @classmethod
     def load(cls, **kwargs):
         """Instantiate and load the cassette stored at the specified path."""
@@ -166,13 +191,14 @@ class Cassette(object):
     def __init__(self, path, serializer=yamlserializer, record_mode='once',
                  match_on=(uri, method), before_record_request=None,
                  before_record_response=None, custom_patches=(),
-                 inject=False):
+                 inject=False, similarity_scorer_factory=None):
 
         self._path = path
         self._serializer = serializer
         self._match_on = match_on
         self._before_record_request = before_record_request or (lambda x: x)
         self._before_record_response = before_record_response or (lambda x: x)
+        self._similarity_scorer_factory = similarity_scorer_factory or SimilarityScorer
         self.inject = inject
         self.record_mode = record_mode
         self.custom_patches = custom_patches
@@ -227,6 +253,20 @@ class Cassette(object):
             if requests_match(request, stored_request, self._match_on):
                 yield index, response
 
+    def failing_matchers(self, a, b):
+        return [matcher for matcher in self._match_on if not matcher(a, b)]
+
+    def similar_requests(self, request):
+        scorer = self._similarity_scorer_factory(self._match_on, request).score
+        scored_requests = [
+            (
+                stored_request,
+                scorer(stored_request, self.play_counts[index])
+            )
+            for index, (stored_request, response) in enumerate(self.data)
+        ]
+        return sorted(scored_requests, key=operator.itemgetter(1), reverse=True)
+
     def can_play_response_for(self, request):
         request = self._before_record_request(request)
         return request and request in self and \
@@ -239,7 +279,7 @@ class Cassette(object):
         hasn't been played back before, and mark it as played
         """
         for index, response in self._responses(request):
-            if self.play_counts[index] == 0:
+            if self.play_counts[index] < self.max_playcount:
                 self.play_counts[index] += 1
                 return response
         # The cassette doesn't contain the request asked for.
diff --git a/vcr/stubs/__init__.py b/vcr/stubs/__init__.py
index e140945..ed575d2 100644
--- a/vcr/stubs/__init__.py
+++ b/vcr/stubs/__init__.py
@@ -227,12 +227,26 @@ class VCRConnection(object):
             if self.cassette.write_protected and self.cassette.filter_request(
                 self._vcr_request
             ):
+                most_similar_request = None
+                failing_matchers = None
+                most_similar_request_info = None
+                try:
+                    most_similar_request_info = self.cassette.similar_requests(self._vcr_request)
+                    most_similar_request = most_similar_request_info[0][0]
+                    failing_matchers = self.cassette.failing_matchers(
+                        self._vcr_request, most_similar_request
+                    )
+                except Exception as err:
+                    print "XXXX {0}".format(err)
+                    import ipdb; ipdb.set_trace()
                 raise CannotOverwriteExistingCassetteException(
                     "No match for the request (%r) was found. "
                     "Can't overwrite existing cassette (%r) in "
-                    "your current record mode (%r)."
+                    "your current record mode (%r). Most similar request was (%r). "
+                    "It differed from the request according to (%r). \n\n\n(%r)"
                     % (self._vcr_request, self.cassette._path,
-                       self.cassette.record_mode)
+                       self.cassette.record_mode, most_similar_request,
+                       failing_matchers, most_similar_request_info)
                 )
 
             # Otherwise, we should send the request, then get the response