Strudel WebMCP

Live-code together.

One of four entries Allison submitted to OpenAI's WebMCP Challenge on 3 September 2026, with the winning JupyterLite WebMCP, Swagger UI WebMCP and Careers WebMCP. It was the last of the four to go in, about 45 minutes before the original deadline.

Strudel is a live-coding environment for music in the browser. Strudel WebMCP wraps the official Strudel REPL and gives a browser agent 13 WebMCP tools over the live, unsaved editor buffer and the running scheduler. You can drag an inline slider while the agent rewrites a different line.

Sharing a buffer with a performer

• Stale edits lose. Every tool that changes the code needs the hash from a fresh read, or it fails with STALE_CODE. That includes your slider drags, because Strudel sliders rewrite numeric literals in the source, and there's a Playwright test for exactly that case.
• You set the dial. The header has Read, Review and Live modes, and only the human can change them. In Review mode the agent's edits become proposals with a diff that you can audition before you accept or discard them.
• The agent gets ears. strudel_record captures the page's own audio output, per voice if you tag it, with levels and frequency-band analysis, and leaves a playable take in the page. Two other tools work against the sound registry the scheduler actually uses.
• Same path as you. Agent edits are evaluated through Strudel's normal Update path, so they become audible exactly the way yours do.

A provenance bug in strudel_record's code hash was fixed after the submission, during the deadline extension.

Try it

The live demo works as a plain Strudel REPL; press Play for sound. The agent tools need ChatGPT's in-app browser or Chrome with experimental web platform features turned on.

The live demo, captured September 2026.

There's a demo video, with a music bed recorded from the app's own audio, and the Devpost entry. AGPL-3.0, because it embeds Strudel; credit for the REPL itself goes to the Strudel project.