diff --git a/changelog.d/4494.misc b/changelog.d/4494.misc
new file mode 100644
index 0000000000..43f8963614
--- /dev/null
+++ b/changelog.d/4494.misc
@@ -0,0 +1 @@
+Add infrastructure to support different event formats
diff --git a/synapse/events/validator.py b/synapse/events/validator.py
index cf184748a1..c53bf44e51 100644
--- a/synapse/events/validator.py
+++ b/synapse/events/validator.py
@@ -21,17 +21,22 @@ from synapse.types import EventID, RoomID, UserID
 
 
 class EventValidator(object):
+    def validate_new(self, event):
+        """Validates the event has roughly the right format
+
+        Args:
+            event (FrozenEvent)
+        """
+        self.validate_builder(event)
 
-    def validate(self, event):
         EventID.from_string(event.event_id)
-        RoomID.from_string(event.room_id)
 
         required = [
-            # "auth_events",
+            "auth_events",
             "content",
-            # "hashes",
+            "hashes",
             "origin",
-            # "prev_events",
+            "prev_events",
             "sender",
             "type",
         ]
@@ -41,8 +46,25 @@ class EventValidator(object):
                 raise SynapseError(400, "Event does not have key %s" % (k,))
 
         # Check that the following keys have string values
-        strings = [
+        event_strings = [
             "origin",
+        ]
+
+        for s in event_strings:
+            if not isinstance(getattr(event, s), string_types):
+                raise SynapseError(400, "'%s' not a string type" % (s,))
+
+    def validate_builder(self, event):
+        """Validates that the builder/event has roughly the right format. Only
+        checks values that we expect a proto event to have, rather than all the
+        fields an event would have
+
+        Args:
+            event (EventBuilder|FrozenEvent)
+        """
+
+        strings = [
+            "room_id",
             "sender",
             "type",
         ]
@@ -54,22 +76,7 @@ class EventValidator(object):
             if not isinstance(getattr(event, s), string_types):
                 raise SynapseError(400, "Not '%s' a string type" % (s,))
 
-        if event.type == EventTypes.Member:
-            if "membership" not in event.content:
-                raise SynapseError(400, "Content has not membership key")
-
-            if event.content["membership"] not in Membership.LIST:
-                raise SynapseError(400, "Invalid membership key")
-
-        # Check that the following keys have dictionary values
-        # TODO
-
-        # Check that the following keys have the correct format for DAGs
-        # TODO
-
-    def validate_new(self, event):
-        self.validate(event)
-
+        RoomID.from_string(event.room_id)
         UserID.from_string(event.sender)
 
         if event.type == EventTypes.Message:
@@ -86,9 +93,16 @@ class EventValidator(object):
         elif event.type == EventTypes.Name:
             self._ensure_strings(event.content, ["name"])
 
+        elif event.type == EventTypes.Member:
+            if "membership" not in event.content:
+                raise SynapseError(400, "Content has not membership key")
+
+            if event.content["membership"] not in Membership.LIST:
+                raise SynapseError(400, "Invalid membership key")
+
     def _ensure_strings(self, d, keys):
         for s in keys:
             if s not in d:
                 raise SynapseError(400, "'%s' not in content" % (s,))
             if not isinstance(d[s], string_types):
-                raise SynapseError(400, "Not '%s' a string type" % (s,))
+                raise SynapseError(400, "'%s' not a string type" % (s,))
diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py
index 5adbe7b538..adf59db7a8 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -2282,7 +2282,7 @@ class FederationHandler(BaseHandler):
             room_version = yield self.store.get_room_version(room_id)
             builder = self.event_builder_factory.new(room_version, event_dict)
 
-            EventValidator().validate_new(builder)
+            EventValidator().validate_builder(builder)
             event, context = yield self.event_creation_handler.create_new_client_event(
                 builder=builder
             )
@@ -2291,6 +2291,8 @@ class FederationHandler(BaseHandler):
                 room_version, event_dict, event, context
             )
 
+            EventValidator().validate_new(event)
+
             try:
                 yield self.auth.check_from_context(room_version, event, context)
             except AuthError as e:
@@ -2376,10 +2378,11 @@ class FederationHandler(BaseHandler):
             # auth check code will explode appropriately.
 
         builder = self.event_builder_factory.new(room_version, event_dict)
-        EventValidator().validate_new(builder)
+        EventValidator().validate_builder(builder)
         event, context = yield self.event_creation_handler.create_new_client_event(
             builder=builder,
         )
+        EventValidator().validate_new(event)
         defer.returnValue((event, context))
 
     @defer.inlineCallbacks
diff --git a/synapse/handlers/message.py b/synapse/handlers/message.py
index 67b364a6c3..05d1370c18 100644
--- a/synapse/handlers/message.py
+++ b/synapse/handlers/message.py
@@ -288,7 +288,7 @@ class EventCreationHandler(object):
 
         builder = self.event_builder_factory.new(room_version, event_dict)
 
-        self.validator.validate_new(builder)
+        self.validator.validate_builder(builder)
 
         if builder.type == EventTypes.Member:
             membership = builder.content.get("membership", None)
@@ -326,6 +326,8 @@ class EventCreationHandler(object):
             prev_events_and_hashes=prev_events_and_hashes,
         )
 
+        self.validator.validate_new(event)
+
         defer.returnValue((event, context))
 
     def _is_exempt_from_privacy_policy(self, builder, requester):