diff --git a/contrib/catapipe.py b/contrib/catapipe.py
new file mode 100644
--- /dev/null
+++ b/contrib/catapipe.py
@@ -0,0 +1,85 @@
+#!/usr/bin/env python3
+#
+# Copyright 2018 Google LLC.
+#
+# This software may be used and distributed according to the terms of the
+# GNU General Public License version 2 or any later version.
+"""Tool read primitive events from a pipe to produce a catapult trace.
+
+For now the event stream supports
+
+  START $SESSIONID ...
+
+and
+
+  END $SESSIONID ...
+
+events. Everything after the SESSIONID (which must not contain spaces)
+is used as a label for the event. Events are timestamped as of when
+they arrive in this process and are then used to produce catapult
+traces that can be loaded in Chrome's about:tracing utility. It's
+important that the event stream *into* this process stay simple,
+because we have to emit it from the shell scripts produced by
+run-tests.py.
+
+Typically you'll want to place the path to the named pipe in the
+HGCATAPULTSERVERPIPE environment variable, which both run-tests and hg
+understand.
+"""
+from __future__ import absolute_import, print_function
+
+import argparse
+import datetime
+import json
+import os
+
+_TYPEMAP = {
+    'START': 'B',
+    'END': 'E',
+}
+
+_threadmap = {}
+
+def main():
+    parser = argparse.ArgumentParser()
+    parser.add_argument('pipe', type=str, nargs=1,
+                        help='Path of named pipe to create and listen on.')
+    parser.add_argument('output', default='trace.json', type=str, nargs='?',
+                        help='Path of named pipe to create and listen on.')
+    parser.add_argument('--debug', default=False, action='store_true',
+                        help='Print useful debug messages')
+    args = parser.parse_args()
+    fn = args.pipe[0]
+    os.mkfifo(fn)
+    try:
+        with open(fn) as f, open(args.output, 'w') as out:
+            out.write('[\n')
+            start = datetime.datetime.now()
+            while True:
+                ev = f.readline().strip()
+                if not ev:
+                    continue
+                now = datetime.datetime.now()
+                if args.debug:
+                    print(ev)
+                verb, session, label = ev.split(' ', 2)
+                if session not in _threadmap:
+                    _threadmap[session] = len(_threadmap)
+                pid = _threadmap[session]
+                ts_micros = (now - start).total_seconds() * 1000000
+                out.write(json.dumps(
+                    {
+                        "name": label,
+                        "cat": "misc",
+                        "ph": _TYPEMAP[verb],
+                        "ts": ts_micros,
+                        "pid": pid,
+                        "tid": 1,
+                        "args": {}
+                    }))
+                out.write(',\n')
+    finally:
+        os.unlink(fn)
+
+if __name__ == '__main__':
+    main()