diff --git a/synapse/api/events/validator.py b/synapse/api/events/validator.py
new file mode 100644
index 000000000..59b486d6d
--- /dev/null
+++ b/synapse/api/events/validator.py
@@ -0,0 +1,81 @@
+# -*- coding: utf-8 -*-
+# Copyright 2014 OpenMarket Ltd
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from synapse.api.errors import SynapseError, Codes
+
+
+class EventValidator(object):
+    def __init__(self, hs):
+        pass
+
+    def validate(self, event):
+        """Checks the given JSON content abides by the rules of the template.
+
+        Args:
+            content : A JSON object to check.
+            raises: True to raise a SynapseError if the check fails.
+        Returns:
+            True if the content passes the template. Returns False if the check
+            fails and raises=False.
+        Raises:
+            SynapseError if the check fails and raises=True.
+        """
+        # recursively call to inspect each layer
+        err_msg = self._check_json_template(
+            event.content,
+            event.get_content_template()
+        )
+        if err_msg:
+            raise SynapseError(400, err_msg, Codes.BAD_JSON)
+        else:
+            return True
+
+    def _check_json_template(self, content, template):
+        """Check content and template matches.
+
+        If the template is a dict, each key in the dict will be validated with
+        the content, else it will just compare the types of content and
+        template. This basic type check is required because this function will
+        be recursively called and could be called with just strs or ints.
+
+        Args:
+            content: The content to validate.
+            template: The validation template.
+        Returns:
+            str: An error message if the validation fails, else None.
+        """
+        if type(content) != type(template):
+            return "Mismatched types: %s" % template
+
+        if type(template) == dict:
+            for key in template:
+                if key not in content:
+                    return "Missing %s key" % key
+
+                if type(content[key]) != type(template[key]):
+                    return "Key %s is of the wrong type (got %s, want %s)" % (
+                        key, type(content[key]), type(template[key]))
+
+                if type(content[key]) == dict:
+                    # we must go deeper
+                    msg = self._check_json(content[key], template[key])
+                    if msg:
+                        return msg
+                elif type(content[key]) == list:
+                    # make sure each item type in content matches the template
+                    for entry in content[key]:
+                        msg = self._check_json(entry, template[key][0])
+                        if msg:
+                            return msg
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