diff --git a/README.md b/README.md
index 445cf6a..5784e93 100644
--- a/README.md
+++ b/README.md
@@ -43,6 +43,14 @@
    - Manually tested against [Mastodon](https://github.com/tootsuite/mastodon)
    - Project is running an up-to-date instance
 
+## ActivityPub
+
+microblog.pub implements an [ActivityPub](http://activitypub.rocks/) server, it implements both the client to server API and the federated server to server API.
+
+Compatible with [Mastodon](https://github.com/tootsuite/mastodon) (which is not following the spec closely), but will drop OStatus messages.
+
+Activities are verified using HTTP Signatures or by fetching the content on the remote server directly.
+
 ## Running your instance
 
 ### Installation
diff --git a/activitypub.py b/activitypub.py
index 5cf1bee..f1de0a8 100644
--- a/activitypub.py
+++ b/activitypub.py
@@ -4,13 +4,13 @@ import os
 from datetime import datetime
 from enum import Enum
 
-import requests
 from bson.objectid import ObjectId
 from html2text import html2text
 from feedgen.feed import FeedGenerator
 
 from utils.linked_data_sig import generate_signature
 from utils.actor_service import NotAnActorError
+from utils import activitypub_utils
 from config import USERNAME, BASE_URL, ID
 from config import CTX_AS, CTX_SECURITY, AS_PUBLIC
 from config import KEY, DB, ME, ACTOR_SERVICE
@@ -936,46 +936,7 @@ def parse_collection(payload: Optional[Dict[str, Any]] = None, url: Optional[str
         return [doc['remote_actor'] for doc in DB.following.find()]
 
     # Go through all the pages
-    out: List[str] = []
-    if url:
-        resp = requests.get(url, headers={'Accept': 'application/activity+json'})
-        resp.raise_for_status()
-        payload = resp.json()
-
-    if not payload:
-        raise ValueError('must at least prove a payload or an URL')
-
-    if payload['type'] in ['Collection', 'OrderedCollection']:
-        if 'orderedItems' in payload:
-            return payload['orderedItems']
-        if 'items' in payload:
-            return payload['items']
-        if 'first' in payload:
-            if 'orderedItems' in payload['first']:
-                out.extend(payload['first']['orderedItems'])
-            if 'items' in payload['first']:
-                out.extend(payload['first']['items'])
-            n = payload['first'].get('next')
-            if n:
-                out.extend(parse_collection(url=n))
-        return out
-
-    while payload:
-        if payload['type'] in ['CollectionPage', 'OrderedCollectionPage']:
-            if 'orderedItems' in payload:
-                out.extend(payload['orderedItems'])
-            if 'items' in payload:
-                out.extend(payload['items'])
-            n = payload.get('next')
-            if n is None:
-                break
-            resp = requests.get(n, headers={'Accept': 'application/activity+json'})
-            resp.raise_for_status()
-            payload = resp.json()
-        else:
-            raise Exception('unexpected activity type {}'.format(payload['type']))
-
-    return out
+    return activitypub_utils.parse_collection(payload, url)
 
 
 def build_ordered_collection(col, q=None, cursor=None, map_func=None, limit=50, col_name=None):
diff --git a/config.py b/config.py
index 6cb17e6..5bbebe5 100644
--- a/config.py
+++ b/config.py
@@ -4,6 +4,7 @@ import yaml
 from pymongo import MongoClient
 import requests
 
+from utils import strtobool
 from utils.key import Key
 from utils.actor_service import ActorService
 from utils.object_service import ObjectService
@@ -20,6 +21,9 @@ except ModuleNotFoundError:
 
 VERSION = subprocess.check_output(['git', 'describe', '--always']).split()[0].decode('utf-8')
 
+DEBUG_MODE = strtobool(os.getenv('MICROBLOGPUB_DEBUG', 'false'))
+
+
 CTX_AS = 'https://www.w3.org/ns/activitystreams'
 CTX_SECURITY = 'https://w3id.org/security/v1'
 AS_PUBLIC = 'https://www.w3.org/ns/activitystreams#Public'
diff --git a/tests/federation_test.py b/tests/federation_test.py
index 20203de..f291638 100644
--- a/tests/federation_test.py
+++ b/tests/federation_test.py
@@ -53,6 +53,11 @@ class Instance(object):
 
         return resp.json()['first']['orderedItems']
 
+    def outbox(self):
+        resp = self.session.get(f'{self.host_url}/following', headers={'Accept': 'application/activity+json'})
+        resp.raise_for_status()
+        return resp.json()
+
 
 def test_federation():
     """Ensure the homepage is accessible."""
diff --git a/utils/activitypub_utils.py b/utils/activitypub_utils.py
new file mode 100644
index 0000000..0275f54
--- /dev/null
+++ b/utils/activitypub_utils.py
@@ -0,0 +1,65 @@
+from typing import Optional, Dict, List, Any
+
+import requests
+
+from .errors import RecursionLimitExceededError
+from .errors import UnexpectedActivityTypeError
+
+
+def _do_req(url: str, headers: Dict[str, str]) -> Dict[str, Any]:
+    resp = requests.get(url, headers=headers)
+    resp.raise_for_status()
+    return resp.json()
+
+
+def parse_collection(
+    payload: Optional[Dict[str, Any]] = None,
+    url: Optional[str] = None,
+    user_agent: Optional[str] = None,
+    level: int = 0,
+    do_req: Any = _do_req,
+) -> List[str]:
+    """Resolve/fetch a `Collection`/`OrderedCollection`."""
+    if level > 3:
+        raise RecursionLimitExceededError('recursion limit exceeded')
+
+    # Go through all the pages
+    headers = {'Accept': 'application/activity+json'}
+    if user_agent:
+        headers['User-Agent'] = user_agent
+
+    out: List[str] = []
+    if url:
+        payload = do_req(url, headers) 
+    if not payload:
+        raise ValueError('must at least prove a payload or an URL')
+
+    if payload['type'] in ['Collection', 'OrderedCollection']:
+        if 'orderedItems' in payload:
+            return payload['orderedItems']
+        if 'items' in payload:
+            return payload['items']
+        if 'first' in payload:
+            if 'orderedItems' in payload['first']:
+                out.extend(payload['first']['orderedItems'])
+            if 'items' in payload['first']:
+                out.extend(payload['first']['items'])
+            n = payload['first'].get('next')
+            if n:
+                out.extend(parse_collection(url=n, user_agent=user_agent, level=level+1, do_req=do_req))
+        return out
+
+    while payload:
+        if payload['type'] in ['CollectionPage', 'OrderedCollectionPage']:
+            if 'orderedItems' in payload:
+                out.extend(payload['orderedItems'])
+            if 'items' in payload:
+                out.extend(payload['items'])
+            n = payload.get('next')
+            if n is None:
+                break
+            payload = do_req(n, headers)
+        else:
+            raise UnexpectedActivityTypeError('unexpected activity type {}'.format(payload['type']))
+
+    return out
diff --git a/utils/errors.py b/utils/errors.py
new file mode 100644
index 0000000..31e678e
--- /dev/null
+++ b/utils/errors.py
@@ -0,0 +1,15 @@
+
+class Error(Exception):
+    pass
+
+
+class BadActivityError(Error):
+    pass
+
+
+class RecursionLimitExceededError(BadActivityError):
+    pass
+
+
+class UnexpectedActivityTypeError(BadActivityError):
+    pass