Change the code. See the effect.
These are real JavaScript mod hooks. The replay uses synthetic tool events and a small, documented API adapter. It is not Claude Code running in the browser.
A WORKBENCH FOR CLAUDE CODE MODS
Build mods you can understand.
Edit real hooks. Replay a session. See what changes.
From a curious idea to an inspectable plugin, right here.
Session replaySIMULATED
—tool calls
—failures
—mock time
EVENT TRACEINPUT → HOOK → RESULT
Run a replay to see your mod in action.
MOD OUTPUT AbovePrompt / Spinner
Your mod's UI will appear here.
A simulated session. No model calls or shell commands.
CAPABILITY LENS
Inspecting source…
FROM REPLAY TO REAL SESSION
Small hooks.
Visible consequences.
OpenMod is an independent experiment by Jerry Wang in making agent extensions easier to inspect.
Understand what you’re installing.
The capability lens finds literal hook registrations and API calls. It is a source inspection aid, not a security audit. Actual Claude Code mods run with your permissions.
Take the source with you.
Download a complete plugin, inspect it, then validate and test it in Claude Code 2.1.287 or later. All three bundled plugins pass the official validator; Flight Recorder also passes four native tests.
claude plugin validate ./flight-recorder
claude --plugin-dir ./flight-recorderTHE ENGINEERING
A lab, with the limitations in the open.
The replay implements tool.call, a subset of ui.render, and UI text resolution. Timings and tool results are fixtures. Unsupported APIs fail explicitly. Source is evaluated in a disposable worker inside a sandboxed frame, with network access blocked and a two-second deadline.