Moontide

Moontide

The moon guides the tide.

A hobby project: Claude plays live music for you. Describe a mood, a theme or an idea, and Claude writes [Strudel](https://strudel.cc) code that plays in your browser and changes without ever stopping.

▶ Watch the demo on YouTube (3 minutes, with sound)

How this was made

Moontide is a personal project. Most of the code, research and documentation was written by an AI coding assistant working under my direction. I set the goals, listened to every change, tried it on my own instruments, judged the results by ear, and made the decisions. I am responsible for what is here, errors included.

Why

Curiosity. I wanted to see how far an AI assistant can go at making real music, not a technical demo, when it is given a good instrument. Strudel is that instrument: a live-coding language where a change lands on the next cycle, with no cut, and where the music is plain text that both of us can read.

So Claude writes the code, and the code stays on screen while it plays. You can watch it, edit it by hand, go back to any earlier version, or point at something in the page and ask for a change.

What it does

• You talk ("start something dreamy in D minor", "darker", "add a bass"). Claude writes Strudel code, and a browser page plays it at once. Each change takes over within a fraction of a second, without stopping the music.
• The code is always visible and editable. Every version that played is kept, and Claude can bring any of them back.
• Around the code, the page shows the music in several views: the named tracks on a timeline where you can edit notes, the Song grid with the sections of a piece, the history as a list or a tree, a mixer with groups and lights whose moves rewrite the code, and a jam view with the scale on a piano or a guitar. When the notes fit several scales, the jam view proposes one and says why.
• Claude can move the tempo up or down over a number of bars, instead of jumping.
• A right-click on anything in the page sends Claude a request with that context. The Requests list in the top bar shows what became of each request.
• The same code can play real MIDI instruments from the page, through Web MIDI.

Moontide does not start from scratch. The music engine is [Strudel](https://strudel.cc), the JavaScript port of TidalCycles by Felix Roos, Alex McLean and the Strudel contributors. Moontide is the bridge between Claude and a Strudel page.

How it works

 you ──talk──► Claude ──MCP (stdio)──► Moontide ──WebSocket (localhost)──► browser page

│ Strudel plays └─ history file on your disk the code, sound and Web MIDI out

1. Moontide runs as an MCP server that Claude connects to. It starts nothing until you ask for music or say "start Moontide".
2. It then opens a page in your browser with a Strudel editor.
3. Claude writes the code, the page plays it, and you watch the code come alive.
4. Claude can stop the music at any point. The page has its own Play and Stop button too.
5. Right-click anything in the page to ask Claude about it. A right-click on the Timeline also sends the moment under the pointer: the cycle and the beat, the version that was playing, and the notes sounding there or starting in the same sixteenth, with their velocities and, for a MIDI track, its instrument and channel. The Session drawer (the Session button in the top bar) says whether page requests are live (they reach Claude right away) or wait for Claude (they reach it with its next action). Its (i) explains how to switch.

The Requests button in the top bar counts the requests still in flight and opens a list: one row per request, with what happened to it and how long ago. A request reads Sent, then Waiting for Claude's next action or Received, then Claude has started on it, which means Claude made a call after the request arrived. A change made for it reads Waiting for its line while it waits for the next bar or phrase, then Applied as v12 (the version in the History view); a change that failed reads Failed with the error, and one that a newer change replaced or Stop canceled says so. A request Claude answers in words reads Answered or Declined, with Claude's sentence. A request shows as applied only when Claude names it with its change, never from timing alone. After 30 seconds without news a row reads No change yet and keeps counting: that is not a failure. If the page loses its connection, open rows read Connection lost. Click a row to see the whole request and what its state means. Finished rows move to a short Recent list after 30 seconds. Nothing is kept after the Moontide server stops.

Install

The short version, for someone who already has Node 22 or later and Claude Code:

claude mcp add --scope user moontide -- npx -y moontide-mcp

Then start a new Claude session and ask for music. The steps below explain each part.

1. What you need

• Node 22 or later, with npm and npx (they come with Node).
• Claude Code or Claude Desktop. Moontide is an MCP server: Claude talks to it.
• Chrome, the browser Moontide was tried with. For MIDI (Web MIDI), use Chrome or Edge.
• Internet access: Strudel and its sounds load from the web.
• Speakers or headphones.

2. Check Node

In a terminal, run:

node --version

It must print v22 or higher. If Node is missing or older, install the LTS version from nodejs.org. On macOS with Homebrew, brew install node works too. Open a new terminal afterwards and check again.

3. Get Claude

Install Claude Code or Claude Desktop from claude.com and sign in once. Moontide works with either; Claude Code is the one tried most.

4. Add Moontide to Claude

Claude Code (tested on macOS; Linux untested)

In a terminal, run:

claude mcp add --scope user moontide -- npx -y moontide-mcp

With --scope user, Moontide is available in every folder. The default scope (local) works only in the folder where you ran the command, and the scope project shares it through a .mcp.json file.

Keep the name moontide. The page-request commands below use it.

Check the install with:

claude mcp get moontide

The same line is meant for Linux. It is untested there.

Claude Desktop (tested on macOS; Windows untested)

Open Settings, then Developer, then Edit Config. The file is:

• macOS: ~/Library/Application Support/Claude/claude_desktop_config.json
• Windows: %APPDATA%\Claude\claude_desktop_config.json

Add Moontide to it:

{

"mcpServers": { "moontide": { "command": "npx", "args": ["-y", "moontide-mcp"] } } }

If the file already has an mcpServers block, add the moontide entry inside it. Quit Claude Desktop fully and start it again. Claude Desktop has no Linux version.

Windows with Claude Code (untested)

From PowerShell or Command Prompt (not Git Bash), run:

claude mcp add --scope user moontide -- cmd /c npx -y moontide-mcp

Check it with claude mcp get moontide. The command must read cmd with /c npx -y moontide-mcp. If it shows C:/ instead of /c, edit the moontide entry in the .claude.json file of your user folder so it reads "command": "cmd", "args": ["/c", "npx", "-y", "moontide-mcp"].

This form comes from community reports. It has not been tried here.

From the source code

To run Moontide from a copy of this repository instead of npm:

git clone https://github.com/konni-arcadia/moontide.git

cd moontide npm ci npm run build

Then add it with the full path of dist/index.js, written here as :

claude mcp add --scope user moontide -- node <folder>/dist/index.js

npm test runs the test suite. The real-browser checks (npm run probe:page) need Chrome.

5. First music

1. Start a new Claude session. Nothing opens yet: Moontide waits until you want it.
2. Ask for music, for example "Play something calm to start the day" or "Give me a slow, warm groove". Or say "start Moontide". In Claude Code, /mcp__moontide__start does the same.
3. The page opens in a new tab at http://localhost:5757, or on another port when 5757 is busy. Claude's replies name the address. The tab title names the folder Claude runs in and the port, for example "Moontide · my-project · 5757".
4. Click once anywhere in the page. Browsers start sound only after a click.
5. Ask for changes: "darker", "add a bass", "slower".

Set MOONTIDE_NO_BROWSER=1 in the environment and starting Moontide opens no tab. Open the address from Claude's reply yourself.

Update

To see the version that runs, run npx -y moontide-mcp --version. Releases are listed in CHANGELOG.md. npx can keep using a copy it already downloaded; to move to the newest release, add Moontide again with @latest:

claude mcp remove moontide --scope user

claude mcp add --scope user moontide -- npx -y moontide-mcp@latest

Uninstall

claude mcp remove moontide --scope user

In Claude Desktop, remove the moontide entry from the config file and restart it. Moontide keeps its history and settings in your data folder (see History); delete that folder if you want them gone too.

MIDI instruments (optional)

Moontide can play MIDI instruments from the code through Web MIDI. It ships ready models for the Roland MT-32 and SC-55. You can describe your own instruments and models, add sound catalogs and send MIDI clock. The setup is in docs/midi.md.

Page requests without a permission prompt

In the Code tab of the Claude app, ask Claude to turn page requests on or off. Claude calls Moontide's set_page_requests tool. In Claude Code in a terminal, type /mcp__moontide__page-requests-on to make them live or /mcp__moontide__page-requests-off to make them wait. Live, Claude starts a monitor, which lasts at most 30 minutes and is started again when a tool reply asks. Waiting, tool replies stop offering to start it until page requests are turned on again. Page requests need an open page, so start Moontide first. These names assume the server was added as moontide.

Claude Code asks permission before it starts the monitor for page requests, because it runs a command. You can approve it each time. If you want a narrower permission rule instead, see the permissions section of the Claude Code documentation. Do not allow broad node commands.

Musical reference

Claude gets a factual reference of the exact Strudel version the page runs, through the get_strudel_reference tool (also offered as MCP resources), covering nine topics: Strudel vs TidalCycles, mini-notation, pattern functions, effects and sound controls, the sound palette, music theory in Strudel, transitions, song structure, and MIDI output. It holds facts only: what exists and how to write it. Moontide ships no mood vocabulary, no style material and no model pieces; Cl