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figcraft/docs/control-protocol.md
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Brandon ThomasandClaude Opus 5.5 b36fd771ab M0.9: MCP server + figcraft-cli, PDF export, web app, release/CI packaging, vector edit mode, workspace lint cleanup
- crates/mcp: JSON-RPC MCP server (18 tools, resources, prompts), headless and attached backends, end-to-end agent tests
- apps/figcraft-cli: info/export/convert/render/run/commands/mcp/perf
- crates/pdf: vector PDF export via krilla with embedded text; file.exportFramesPdf
- apps/figcraft-web + packaging/{macos,windows,linux,freebsd,web} + release/ci workflows
- engine vectoredit: edit points/handles/bend/add/delete-heal; canvas overlay and edit strip

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
2026-10-09 13:31:53 -04:00

120 lines
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# FigCraft control protocol
The desktop app can be driven by other programs (tests, scripts, `figcraft-cli mcp --attach`,
sibling Crafting Apps) through a loopback socket:
```sh
cargo run -p figcraft -- --control 7979 [file.figcraft|file.svg|image]
```
The app listens on `127.0.0.1:<port>` only. Each connection carries **newline-delimited JSON**:
one request object per line, one reply line per request, in order.
```text
request: {"id": 1, "method": "engine.execute", "params": {...}}
reply: {"id": 1, "ok": true, "result": ...}
{"id": 1, "ok": false, "error": "message"}
```
Requests are queued and run on the UI thread at the start of the next frame, so replies reflect the
real UI state. A request that the UI doesn't answer within 60 s gets a timeout error. A line that is
not JSON gets `{"id": null, "ok": false, "error": "bad JSON: …"}`. The implementation is in
`crates/ui-egui/src/control.rs` (methods) and `apps/figcraft/src/control_server.rs` (socket).
Coordinates are page units, y down. `x`/`y` in `node.set`/`node.create` are parent-relative.
## Methods
### `engine.execute {command, params?}`
Run any command (the same ids as the menus, shortcuts, Actions palette, CLI and MCP). Programmatic
calls never open dialogs: dialog requests are dropped. Returns the command's result (creation
commands return `{"id": N}`).
```json
{"id":1,"method":"engine.execute","params":{"command":"shape.rectangle","params":{"x":10,"y":10,"width":100,"height":50}}}
{"id":1,"ok":true,"result":{"id":2}}
{"id":2,"method":"engine.execute","params":{"command":"node.set","params":{"ids":[2],"props":{"fill":"#FF6B6B","cornerRadius":8}}}}
{"id":3,"method":"engine.execute","params":{"command":"command.batch","params":{"label":"Tidy","commands":[{"command":"align.left","params":{"ids":[2,3]}},{"command":"distribute.vertical","params":{"ids":[2,3]}}]}}}
```
### `engine.commands {}`
Every command: `[{id, label, params, menu, shortcut, undoable}]`.
### `document.inspect {depth?, allPages?}`
The active document as JSON: name, path, dirty, currentPage, selection, pages (the current page's
layer tree to `depth`, default 8; others summarised unless `allPages`), styles, variable count,
images, the text being edited and the undo history.
### `node.get {id, depth?}`
One layer (children to `depth`, default 1). Fields: id, name, type, x, y, width, height, rotation,
absoluteBounds, visible, locked, opacity, blend, fills, strokes, strokeWeight, effects, cornerRadius,
layout, sizing, constraints, clip, text properties, component/instance links, overrides,
boundVariables, interactions, exports.
### `ui.inspect {}`
UI state: panels and tabs, current tool, canvas rect, dialogs, view, timings.
### `ui.pointer {kind, x, y | sx, sy, to?, steps?, shift?, alt?, cmd?, ctrl?}`
A mouse gesture with the current tool. `kind`: `down`, `move`, `up`, `click`, `double`, `hover`,
`drag` (needs `to: [x, y]`; `steps` intermediate moves, default 8). Position in page coordinates
(`x`, `y`) or screen pixels (`sx`, `sy`). Returns `{selection, tool}`.
```json
{"id":4,"method":"engine.execute","params":{"command":"tool.set","params":{"tool":"ellipse"}}}
{"id":5,"method":"ui.pointer","params":{"kind":"drag","x":200,"y":200,"to":[300,260],"shift":true}}
```
### `ui.key {key, shift?, alt?, cmd?, ctrl?}`
A key as if typed on the canvas: a menu shortcut (`{"key":"G","cmd":true}` groups), a tool key,
`Escape`, `Delete`/`Backspace`, `Enter`, arrows (nudge; shift = big nudge). While text is being
edited, keys go to the text editor. Returns `{"command": id}` for shortcuts.
### `ui.type {text}`
Type into the text being edited (start editing with a double-click, `text.edit.begin {id}`, or the
text tool).
### `ui.menu.invoke {id}`
Invoke a menu item exactly like clicking it (this may open a dialog). Returns `{ok, lastError}`.
### `ui.set {rightTab?, leftTab?, theme?, home?, palette?, mainMenu?}`
Switch panels and modes: `rightTab` `design|prototype|inspect`, `leftTab` `file|assets`, `theme`,
`home` (bool), `palette` (bool: the Actions palette), `mainMenu` (bool). Returns `ui.inspect`.
### `ui.screenshot {path}`
PNG of the whole window, UI included (needs a visible window). Returns `{path, width, height}`.
### `ui.render {path, scale?, ids?}`
PNG of the document without UI chrome (works without a window). Without `ids` it exports the
selection, else the page's top-level layers. Returns the export result.
### `app.quit {}`
Close the app.
## Example session (shell)
```sh
port=7979
figcraft --control $port &
exec 3<>/dev/tcp/127.0.0.1/$port
echo '{"id":1,"method":"engine.execute","params":{"command":"frame.create","params":{"preset":"iPhone 16","x":0,"y":0}}}' >&3
read -r reply <&3; echo "$reply"
echo '{"id":2,"method":"ui.screenshot","params":{"path":"/tmp/figcraft.png"}}' >&3
read -r reply <&3; echo "$reply"
```
For agents, prefer the MCP server (`figcraft-cli mcp --attach 7979`, see `docs/mcp.md`): it wraps
these methods in documented tools and returns images inline.