diff --git a/protocol.py b/protocol.py
index fa847e3..0169fb2 100644
--- a/protocol.py
+++ b/protocol.py
@@ -45,7 +45,19 @@ objects_cache_lock = threading.Lock()
 logger = logging.getLogger(__name__)
 
 
-class Protocol:
+# maps string label to Protocol subclass. populated by ProtocolMeta.
+protocols = {}
+
+class ProtocolMeta(type):
+    """:class:`Protocol` metaclass. Registers all subclasses in the protocols global."""
+    def __new__(meta, name, bases, class_dict):
+        cls = super().__new__(meta, name, bases, class_dict)
+        if cls.LABEL:
+            protocols[cls.LABEL] = cls
+        return cls
+
+
+class Protocol(metaclass=ProtocolMeta):
     """Base protocol class. Not to be instantiated; classmethods only.
 
     Attributes:
diff --git a/tests/test_protocol.py b/tests/test_protocol.py
index 0366a6f..312bcc0 100644
--- a/tests/test_protocol.py
+++ b/tests/test_protocol.py
@@ -5,9 +5,11 @@ from flask import g
 from oauth_dropins.webutil.testutil import requests_response
 import requests
 
+import protocol
 from protocol import Protocol
 from flask_app import app
 from models import Follower, Object, User
+from webmention import Webmention
 
 from .test_activitypub import ACTOR, REPLY
 from . import testutil
@@ -35,6 +37,10 @@ class ProtocolTest(testutil.TestCase):
         self.request_context.pop()
         super().tearDown()
 
+    def test_protocols_global(self):
+        self.assertEqual(FakeProtocol, protocol.protocols['fake'])
+        self.assertEqual(Webmention, protocol.protocols['webmention'])
+
     @patch('requests.get')
     def test_receive_reply_not_feed_not_notification(self, mock_get):
         Follower.get_or_create(ACTOR['id'], 'foo.com')