compositor-mcp

An MCP server that lets Claude and other AI agents read and edit Compositor projects, the open-source Photoshop alternative for Mac.

It works on the documented .comp package format (a manifest.json plus one PNG per layer), so it needs no changes to Compositor itself. Edit a project with an agent, then open it in Compositor. Or the other way round: save in Compositor and let the agent inspect, retouch or render it.

What the agent can do

The server also exposes a compositor://format resource describing the file format.

Related

marcushorndt/compositor-mcp takes a different route: it drives Compositor's own document model and renderer headlessly (Swift), so previews match the app exactly. This package is a plain Node server that works on the documented file format, needs no build of the app, and runs wherever Node runs. Pick whichever fits your setup; both open the same .comp files.

Install

Requires Node.js 20 or later. Compositor itself is only needed to look at the result.

Claude Code

claude mcp add compositor -- npx -y compositor-mcp

Claude Desktop

Add to claude_desktop_config.json:

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

From source

git clone https://github.com/Josusanz/compositor-mcp
cd compositor-mcp
npm install
npm run build
claude mcp add compositor -- node /path/to/compositor-mcp/dist/src/index.js

Example session

Create a 1920×1080 project at ~/Desktop/poster.comp with a white background, add photo.jpg scaled to fill, put logo.png in the bottom right corner at 80 % opacity with Multiply, then show me a preview and open it in Compositor.

The agent calls create_project, add_image_layer twice, set_layer, render_preview and open_in_compositor. Compositor opens the document with the layers ready to keep editing.

How it maps to the Compositor format

• Layer pixels are stored untouched as 8-bit sRGB PNGs; placement, scale, rotation and flips live in the layer transform, so edits stay non-destructive.
• Masks are written as 8-bit grayscale PNGs without alpha, as Compositor requires.
• Manifests are validated against the same rules as ProjectStore.swift before writing, written with sorted keys and replaced atomically.
• Fields this tool does not understand (adjustments, effects, text, shapes, guides, anything newer) are preserved on round trip.
• Projects are saved as format version 9 (what Compositor 1.2.6 writes); a project declaring a newer version keeps its own number and its unknown fields on round trip. Older Compositor builds reject newer versions; update the app if a file will not open.

Limitations

• The preview renderer covers order, folders, visibility, opacity, transforms, raster masks and the blend modes sharp supports. Clipping masks, adjustment layers and layer effects are not rendered yet; the tool reports what it skipped. Compositor's own export is the reference.
• Compositor does not watch files for changes. After the agent edits a project that is already open, close and reopen the document (or call open_in_compositor).
• There is no live connection to the running app: selection, undo history and the viewport are session-only in Compositor and out of reach here.

Development

npm install
npm test        # builds and runs the node:test suite
npm run dev     # runs the server from TypeScript with tsx

License

MIT. Compositor is © Robbie Tilton, also MIT.