figcraft/docs/mcp.md

# FigCraft MCP server

FigCraft ships a [Model Context Protocol](https://modelcontextprotocol.io) server so AI agents can
design with it: create and edit layers, run any menu command, inspect the result as JSON and look at
it as a PNG. It speaks newline-delimited JSON-RPC 2.0 over stdio (MCP protocol `2025-06-18`;
`2025-03-26` and `2024-11-05` clients are accepted too).

The server lives in `crates/mcp` (`figcraft-mcp`) and is started by the CLI:

| Command | Backend |
|---|---|
| `figcraft-cli mcp` | **Headless**: an in-process engine session with one untitled document. No window; renders with the CPU renderer. |
| `figcraft-cli mcp --attach <port>` | **Attached**: drives a running FigCraft app through its control channel (`figcraft --control <port>`). The user sees every change live. |

`--attach` also takes `host:port`. The control channel only listens on 127.0.0.1.

## Configure a client

Build the CLI first (`cargo build --release -p figcraft-cli`) and use the absolute path to
`target/release/figcraft-cli`.

### Claude Code

```sh
# headless
claude mcp add figcraft -- /path/to/figcraft-cli mcp
# drive the running app (start it with: figcraft --control 7979)
claude mcp add figcraft-app -- /path/to/figcraft-cli mcp --attach 7979
```

Or in a project's `.mcp.json`:

```json
{
  "mcpServers": {
    "figcraft": { "command": "/path/to/figcraft-cli", "args": ["mcp"] }
  }
}
```

### Claude Desktop

`claude_desktop_config.json` (Settings > Developer > Edit Config):

```json
{
  "mcpServers": {
    "figcraft": { "command": "/path/to/figcraft-cli", "args": ["mcp"] },
    "figcraft-app": { "command": "/path/to/figcraft-cli", "args": ["mcp", "--attach", "7979"] }
  }
}
```

## Conventions agents must know

- Coordinates are **page units** (1 unit = 1 px at 100% zoom), x right, **y down**.
- `create_node` and `set_properties` take `x`/`y` **relative to the parent** (the page when there is
  no parent, so they are page coordinates then). `inspect_document` reports parent-relative `x`/`y`
  plus `absoluteBounds` in page coordinates.
- Children of an auto-layout frame are positioned by the layout: set `layout`, `gap`, `padding`,
  `mainAlign`, `crossAlign`, `sizingH`/`sizingV` instead of x/y. More auto layout props:
  - `minWidth` / `maxWidth` / `minHeight` / `maxHeight` (px, `null` removes) bound Hug, Fill and
    Fixed sizes; a hugging text wider than its max width wraps.
  - `absolute: true` takes a child out of the flow (it stays where it is and follows its
    `constraints` when the frame resizes; Fill becomes Fixed).
  - `crossAlign: "baseline"` lines up the first text baselines in horizontal layouts (other layers
    align to the top; nested auto layout frames use their first child's baseline).
  - `wrap` with `crossGap` (alias `rowGap`) for the gap between wrapped rows.
  - Grid (`layout: "grid"`): `gridColumns`, `gridRows` (minimum; rows grow), `columnGap` /
    `rowGap`, track sizes `columnTracks` / `rowTracks` as `[120, "1fr", "auto"]` (px fixed, `fr`
    fill share, `auto` hug) or the `layout.setTrack {axis, index, sizing, value?}` command; on a
    child, `gridColumn` / `gridRow` (0-based anchor cell, `null` = placed automatically) and
    `gridColumnSpan` / `gridRowSpan`. `inspect` reports a grid child's resolved `gridCell`.
- **Every menu action is a command** (`list_commands`), and most commands act on `ids` when given,
  else on the selection. New layers become the selection.
- Colours are `"#RRGGBB"` or `"#RRGGBBAA"`. Inside fills, strokes and effects passed through the MCP
  tools, `color` may also be a hex string and gradients can be written
  `{"type": "linearGradient", "stops": ["#7048E8", "#1098AD"]}`; the server converts them to the
  engine's paint JSON.
- Text props (`fontFamily`, `fontStyle`, `fontSize`, `lineHeight`, `letterSpacing`, `textDecoration`,
  `textCase`, `textFills`, `fontVariations`…) apply to the whole layer, or to chars `start`..`end`
  when given (`text.style {id, start, end, …}` does the same). Styled ranges come back as
  `styledRuns`. Variable fonts: `fontVariations` (alias `variationSettings`) sets axis values in
  user units, e.g. `{"wght": 550, "wdth": 85}` (`null` = back to what the style name implies);
  `text.setVariations {variations, replace?}` merges instead. `text.fonts {family, style?, axes: true}`
  lists a font's axes and named instances (named instances are also valid `fontStyle` values).
  OpenType features: `features {"liga": false, "tnum": true}`.
- Every mutation is one undo step (`batch` makes several one step). A failing command leaves the
  document as it was.
- Programmatic calls never open dialogs.
- Verify your work: `inspect_document` / `get_node` for numbers, `screenshot` for pixels.

## Tools

| Tool | What it does |
|---|---|
| `list_commands {filter?}` | Every command: id, label, menu, shortcut, undoable, params doc. |
| `run_command {command, params}` | Run any command (e.g. `align.left`, `layout.add`, `component.create`, `instance.place` (drop an instance at a page point into the frame or auto layout slot under it), `component.exposeInstance` / `instance.exposed` (nested instance properties on instances), `inspect.code` (CSS, SwiftUI or Jetpack Compose for a layer), `style.create`, `variable.bind`, `proto.interaction.add`). |
| `batch {commands: [{command, params}], label?}` | Several commands as one undo step (`command.batch`); all-or-nothing. |
| `create_node {type, x, y, width, height, parent, index, name, text, path, props}` | Create a frame, rectangle, ellipse, polygon, star, line, arrow, text, vector, section, component or slice; returns `{id, node}`. |
| `set_properties {ids, props}` | `node.set` on layers (geometry, fills, strokes, effects, corner radius, auto layout, sizing, constraints, masks (`isMask`, `maskType: alpha\|vector\|luminance`), handoff status (`devStatus: none\|readyForDev\|completed`), text…); returns the updated layers. |
| `inspect_document {depth, allPages}` | The document as JSON (layer tree, styles, selection, history). |
| `get_node {id, depth}` | One layer as JSON. |
| `select {ids}` | Replace the selection (`[]` deselects). |
| `export {ids, format, scale, path?}` | png, jpg, svg, webp (pdf when available). Without `path`, images come back as MCP image content, SVG as text. |
| `screenshot {ids?, scale?, maxSize?, window?}` | PNG of the page (with background) or of layers, scaled to fit `maxSize` (default 1600). `window: true` captures the app window when attached. |
| `open_file {path}` / `save_file {path?}` | Open `.figcraft`, `.json` (FigCraft JSON or REST API file JSON, see below), `.svg` or an image; save as `.figcraft`. |
| `undo` / `redo` | Step through history. |
| `pointer {kind, x, y, to?, steps?, tool?, shift, alt, cmd}` | Mouse gestures in page coordinates with the current tool: `click`, `double`, `drag`, `down`, `move`, `up`, `hover`. |
| `key {key, shift, alt, cmd}` | A shortcut or key as if typed on the canvas (menu shortcuts, tool keys, Escape, Delete, arrows; text editing keys while editing text). |
| `type_text {text, id?}` | Type into the text being edited, or replace the contents of text layer `id`. |
| `inspect_ui {}` | Tool, view and status (and panels/timings when attached). |

### Editing vectors

Vector edit mode is driven with `run_command` (or `pointer`/`key` for gestures):
`vector.edit.begin {id}` (converts shapes to vectors), `vector.edit.state` (page-space overlay, the
local network and each point's handle mirroring), `vector.edit.tool {tool: move|pen|bend|paint|lasso|cut|eraser}`,
`vector.edit.select {vertices?, segments?, add?}`, `vector.edit.selectAll`, `vector.edit.moveVertices`,
`vector.edit.nudge`, `vector.edit.position {x?, y?}`, `vector.edit.setHandle`, `vector.edit.mirroring
{mode: none|angle|angleAndLength}`, `vector.edit.smooth {smooth?}`, `vector.edit.bend`,
`vector.edit.addVertex`, `vector.edit.connect {a, b}`, `vector.edit.pen {x, y, dx?, dy?}` (continues
from the pen's open end; clicking a point connects or branches), `vector.edit.penEnd`,
`vector.edit.paint {x, y}` (paint bucket: fills or unfills the closed area under a page point),
`vector.edit.cut {segment, t} | {vertex}`, `vector.edit.erase {points, radius?}` (the eraser),
`vector.edit.lasso {points}`, `vector.edit.delete`,
`vector.deleteHeal`, `vector.join` / `vector.smoothJoin` (join the selected points while editing),
`vector.edit.cornerRadius`, `vector.edit.end`. Point indices refer to `network.vertices` in
`vector.edit.state`; local coordinates are the layer's own.

### Importing REST API file JSON

The JSON returned by the public REST API's file endpoint (`GET /v1/files/:key`, best with
`geometry=paths` so vectors carry their outlines) and its nodes endpoint opens like any document:
`open_file {path}` (a new, untitled document; the JSON is never saved over) or
`run_command {command: "file.import", params: {path}}` (pages appended to the current document).
The result's `warnings` list what was skipped or approximated (unsupported layer, paint and effect
types, prototype interactions, variable bindings, instances of components outside the file, which
come in as frames). Pages, the layer tree, geometry, paints, strokes, effects, corners, constraints,
auto layout, layout grids, exports, text with styled runs, vectors, components, component sets,
instances and component properties are mapped. Image fills keep their `imageRef` and show a grey
placeholder unless the image files sit in an `images` folder next to the JSON, named by `imageRef`
(`images/<imageRef>.png`); nothing is fetched from the network.

### Version history

Named snapshots of the document, kept in the `.figcraft` file (they persist once the file is saved;
a new, renamed or deleted version marks the file as changed). Driven with `run_command`:
`file.saveVersion {name?, description?}` (returns `{id, index, name, description, time}`; untitled
versions are named "Version N"), `version.list` (oldest first; `time` is Unix seconds),
`version.restore {id | index}` (replaces the document with the version as one undo step; the file
name stays), `version.rename {id | index, name, description?}`, `version.delete {id | index}` and
`version.duplicate {id | index}` (opens the version as a new document tab). Indexes are validated
(a negative or out-of-range index is an error). A file keeps at most 100 versions; there are no
automatic versions. `file.versionHistory` returns the same list and opens the panel in the app.

Tool failures come back as results with `isError: true` and a message; protocol problems (unknown
tool, malformed JSON, wrong parameter types) are JSON-RPC errors. Nothing crashes the server.

## Resources

| URI | Content |
|---|---|
| `figcraft://document` | The active document (like `inspect_document` at depth 8). |
| `figcraft://commands` | The command catalog. |
| `figcraft://node/{id}` (template) | One layer with children to depth 2. |
| `figcraft://command/{id}` (template) | One command's docs, e.g. `figcraft://command/layout.add`. |

## Prompts

| Prompt | Arguments |
|---|---|
| `mobile_screen` | `screen` (required), `device` (default "iPhone 16"), `brand_color` |
| `design_system` | `name`, `primary` |
| `landing_page` | `product` (required), `width` (default 1440), `accent` |
| `prototype_flow` | `screens` (comma-separated), `transition` |

Each returns a step-by-step plan naming the exact tools and commands to use and how to verify.

## Examples

Create a card with auto layout and check it:

```json
{"jsonrpc":"2.0","id":1,"method":"tools/call","params":{"name":"create_node","arguments":{
  "type":"frame","name":"Card","x":100,"y":100,"width":320,
  "props":{"fill":"#FFFFFF","cornerRadius":16,"layout":"vertical","padding":24,"gap":12,"sizingV":"hug",
           "effects":[{"type":"dropShadow","color":"#00000026","offset":[0,4],"radius":16}]}}}}
{"jsonrpc":"2.0","id":2,"method":"tools/call","params":{"name":"create_node","arguments":{
  "type":"text","parent":2,"text":"Ada Lovelace","props":{"fontSize":24,"fontStyle":"Bold"}}}}
{"jsonrpc":"2.0","id":3,"method":"tools/call","params":{"name":"get_node","arguments":{"id":2,"depth":2}}}
{"jsonrpc":"2.0","id":4,"method":"tools/call","params":{"name":"screenshot","arguments":{"ids":[2]}}}
```

A component with an instance whose text is overridden (ids are the ones earlier calls returned; read
the instance's text layer id with `get_node`):

```json
{"jsonrpc":"2.0","id":5,"method":"tools/call","params":{"name":"run_command","arguments":{"command":"component.create","params":{"ids":[2]}}}}
{"jsonrpc":"2.0","id":6,"method":"tools/call","params":{"name":"run_command","arguments":{"command":"instance.create","params":{"component":2,"x":500,"y":100}}}}
{"jsonrpc":"2.0","id":7,"method":"tools/call","params":{"name":"type_text","arguments":{"id":7,"text":"Grace Hopper"}}}
```

Align and distribute as one undo step:

```json
{"jsonrpc":"2.0","id":8,"method":"tools/call","params":{"name":"batch","arguments":{"label":"Tidy","commands":[
  {"command":"align.top","params":{"ids":[3,4,5]}},
  {"command":"distribute.horizontal","params":{"ids":[3,4,5]}}]}}}
```

The end-to-end tests in `crates/mcp/tests/agent_tasks.rs` are worked examples of ten realistic
tasks (auto layout, components and overrides, gradients and shadows, paint styles, Light/Dark
variables, align/distribute/group, boolean subtract + flatten, export, undo/redo, drawing with tools).