figcraft/docs/control-protocol.md

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:

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.

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}).

{"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 colour profile (colorProfile: srgb or displayP3), 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 (including grid columnTracks / rowTracks), sizing, minWidth / maxWidth / minHeight / maxHeight, absolute, constraints (children of plain frames and absolute children), gridCell (a grid auto layout child's column, row and spans), clip, text properties, component/instance links, overrides, slot (a slot layer's property name), boundVariables, interactions, exports. The auto layout props that node.set accepts are listed in mcp.md.

ui.inspect {}

UI state: panels and tabs, current tool, canvas rect, dialogs, view, timings (frameMs, renderMs) and what the last canvas render had to do (canvas.renderWork: full, partial with the pixels re-rendered after a pan or an edit, or reused). While a prototype plays, presenter (full window) and preview (the preview pane) hold the player's state: the current frame and its name, start, history, open overlays, the screen's scroll offset and scrollRange, the device and the viewport of the frame its screen shows (null when nothing plays).

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}.

{"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 (in vector edit mode the edit keys come first: V P Q X Shift+B tools, arrows nudge points, Delete/Shift+Delete, Cmd+A, Cmd+J; with the shape builder, Enter finishes): a menu shortcut ({"key":"G","cmd":true} groups), a tool key, Escape, Delete/Backspace, Enter, arrows (nudge; shift = big nudge; auto layout children move one place along the flow; with cmd they resize the selection). 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?, colorPicker?, variables?, layerFilter?, collapseLayers?, exportPreview?, preview?, presentScroll?, colorProfileDialog?, stylePicker?, stylePickerEdit?, stylePickerView?}

Switch panels and modes: rightTab design|prototype|inspect, leftTab file|assets, theme, home (bool), palette (bool: the Actions palette), mainMenu (bool), colorPicker ({fills?, index?}: open the colour picker on the selection's paint; null closes it), variables (bool, or a collection id or name to show: the Variables editor), layerFilter (string: open the layers search with that filter; null closes it), collapseLayers (true: collapse the layers tree), exportPreview (bool: the Design panel Export section's preview), preview (true or a frame id: open the prototype preview pane like proto.preview; false or null closes it), presentScroll ([x, y]: scroll the presented screen, the full window's else the pane's, clamped to what it can scroll), colorProfileDialog (srgb|displayP3: open File ▸ Color profile with that profile chosen; null closes it), stylePicker (fill|stroke|effect|grid: open the style picker for the selection; null closes it) with stylePickerEdit (a style id or name: open its editor), stylePickerView (list|grid). Returns ui.inspect (which reports stylePicker and stylePickerView).

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)

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.