diff --git a/contrib/mitmproxy/failures.py b/contrib/mitmproxy/failures.py
new file mode 100644
index 00000000..10dc1898
--- /dev/null
+++ b/contrib/mitmproxy/failures.py
@@ -0,0 +1,47 @@
+"""
+A mitmproxy script that introduces certain request failures in a deterministic
+way.
+
+Used mainly for Matrix style requests.
+
+To run execute it with mitmproxy:
+
+    >>> mitmproxy -s failures.py`
+
+"""
+import time
+import json
+
+from mitmproxy import http
+from mitmproxy.script import concurrent
+
+REQUEST_COUNT = 0
+
+
+@concurrent
+def request(flow):
+    global REQUEST_COUNT
+
+    REQUEST_COUNT += 1
+
+    if REQUEST_COUNT % 2 == 0:
+        return
+    elif REQUEST_COUNT % 3 == 0:
+        flow.response = http.HTTPResponse.make(
+            500,
+            b"Gateway error",
+        )
+    elif REQUEST_COUNT % 7 == 0:
+        if "sync" in flow.request.pretty_url:
+            time.sleep(60)
+        else:
+            time.sleep(30)
+    else:
+        flow.response = http.HTTPResponse.make(
+            429,
+            json.dumps({
+                "errcode": "M_LIMIT_EXCEEDED",
+                "error": "Too many requests",
+                "retry_after_ms": 2000
+            })
+        )