OneCAD/docs/control-protocol.md

Control protocol

solidcraft --control PORT (or SOLIDCRAFT_CONTROL_PORT=PORT) listens on 127.0.0.1:PORT for JSON lines. Each request is one line {"id": …, "method": "…", "params": {…}}; each reply is one line {"id": …, "ok": true, "result": …} or {"id": …, "ok": false, "error": "…"}. Requests are handled on the UI thread between frames; pointer and keyboard input is injected as real egui events, one pointer event per frame.

The channel is untrusted input. A request line may be at most 16 MiB; a longer one is answered with {"ok": false, "error": "request too large"} and the connection is closed, as are connections that send eight lines that are not JSON. At most 16 connections are served at once (further ones get {"ok": false, "error": "too many connections"}), at most 64 queued requests run per frame so a flood cannot starve drawing, and a request that the UI thread has not answered within 60 seconds is replied to with {"ok": false, "error": "timeout"}. The same 16 MiB line limit applies to the MCP server.

Engine

Method	Params	Result
engine.execute	command: command id, params: JSON object	the command's result
engine.script	commands: [{command, params}, …]	results, stops at the first error
engine.commands	—	every command: id, label, tab, panel, icon, shortcut, params doc, enabled
document.inspect	measure?: bool	parameters, timeline (errors, timings), bodies, sketches, selection

Commands never open dialogs when run this way. solidcraft-cli commands prints the same registry.

Every sketch.* command that changes a sketch adds created: {points, curves, constraints, dimensions} to its result (and wires for 3D curves): the ids of what it added, in creation order, next to whatever else the command returns (curves, sides, corners…). Sketch ids are stable and never reused, even after a delete (l1, l2, then l3 once l2 is gone; only undo rolls the numbering back with the design), so they can go straight into later commands:

{"id":7,"method":"engine.execute","params":{"command":"sketch.line","params":{"points":[[0,0],[40,0]]}}}
→ {"curves":["l1"],"created":{"points":["l1.start","l1.end"],"curves":["l1"],"constraints":["k1"],"dimensions":[]},…}
{"id":8,"method":"engine.execute","params":{"command":"sketch.dimension","params":{"entities":["l1"],"value":50}}}

A bare numeric value given to sketch.dimension (from the control channel, scripts or MCP) is read in the design's units, exactly as if it were typed into the dimension box: in an inch design "value": 2 makes the line 2 in (50.8 mm) long. Point coordinates stay in millimetres. To pin a unit regardless of the design, pass an expression with one: "value": "50 mm" or "value": "0.5 in". Angles are degrees unless the expression says otherwise.

UI

Method	Params	Notes
ui.inspect	—	UI state, what is hidden (visibility: bodies, origin and construction items, sketches; set it with the browser.visibility command), viewport rect, camera, active tool/dialog, hover, renderer, timings, live preview (active, busy, error, ms, bodies it stands in for)
ui.set	any UiState field (tab, perspective, showGrid, dark, …), and hiddenBodies, hiddenOrigin, hiddenSketches, shownSketches (whole lists; browser.visibility changes single items)	dark: false switches to the light theme
ui.view	view: front, back, top, bottom, left, right, iso, home, fit; animate (bool, default false: snap)
ui.start	command	like a toolbar click: starts the sketch tool or dialog for the command
ui.click	x, y (screen points), button?: left/right/middle, shift?, ctrl?, double?	real pointer input
ui.move	x, y
ui.drag	x0, y0, x1, y1, button?, shift?, ctrl?, steps?, hold?, hold_end?	press, move, release; a left drag on the model is a box selection (left to right: window, right to left: crossing); with OpenSCAD navigation, plain left-drag on empty space orbits, Shift+left-drag box-selects, and drags starting on sketch geometry edit it; hold keeps the button down that many frames first (a right press-and-hold opens the marking menu, releasing over a direction picks it), hold_end that many frames at the end (a sketch drag shows its snap)
ui.menu	x?, y?, target?, close?	with a point: open a context menu there as a right-click would (the viewport's marking menu, or a browser menu with target: {"type": "body", "name"} | {"type": "sketch", "id"} | {"type": "component", "id"}); without: the open menu (radial and items: id, label, shortcut, enabled)
ui.menuPick	item: id or label	runs an item of the open menu, as clicking it does
ui.selectOther	x?, y?, pick?, add?, hover?, close?	Select Other: with a point, list everything pickable there (as holding the left button does); pick: select row pick (add: as Shift-click; with a dialog open, into its active input); hover: light a row up; without: the open list (open, at, total: everything under the cursor, rows: label, icon, sel, at most 20 per kind, nearest first)
ui.rename	text?, commit? (default true)	finishes the rename box a Rename item opened
ui.selection		the selection, the open dialog's inputs, the hovered item, and the active sketch's drawn dimensions (dimensions: id and text centre, dimension_selected, dimension_editing)
ui.worldToScreen	points: [[x, y, z]…] world points	their screen points
ui.triad		screen points of the 3D sketch move triad's handles (x, y, z, plane)
ui.sketchToScreen	points: [[x, y]…] in active-sketch coordinates	their screen points (null when behind the camera)
ui.dialogInput	index	what clicking an input's Select chip does: picks go to that input
ui.at	world: [x,y,z] | sketch: [x,y] | plane: "XY" | axis: "Z" | dimension: "d1" (its value text) | handle: "arrow" (a manipulator handle, see scenario::publish_handle)	the screen point (a scenario step's target; see crates/ui-egui/src/scenario.rs)
ui.handles	prefix?	the handles drawn last frame, [{name, x, y}]: toolbar buttons and drop-down items toolbar:<command id> (the button alone: button:<command id>; a drop-down row: dropdown:<command id>, highlighted dropdown_hot:<command id>, its pin dropdown_pin:<command id>; Customize Toolbar's check boxes customize:<command id>), panel labels panel:<tab>:<panel>, browser rows row:<label> and fold arrows fold:<label>, manipulator handles; orientation tips axis_view:x, axis_view:-x (and y/z)
ui.editFeature	feature (id or name)	what double-clicking a timeline item does: rolls back to it and opens its dialog filled in (sketches open in sketch mode)
ui.scroll	x, y, delta?	wheel zoom at the cursor
ui.key	key (egui key name, Enter, Escape…), cmd?, shift?
ui.text	text	typed text
ui.screenshot	path?	PNG of the window (needs a presented frame)
ui.render	path, width?, height?	CPU render of the model with the current camera (no window needed); cut by the section the viewport shows (inspect.section, an open Section Analysis dialog's preview, a sketch's Slice), with the cut face capped
ui.confirm	accept?: bool	answers the Delete confirmation (shown when a delete takes other features with it or makes some fail); without accept, what it lists
ui.documents	action?: new, switch, close, quit; index?; force? (close without asking); answer?: save, dont_save, cancel (answers "save changes?")	the open designs (tabs): names, unsaved flags, the active one, a pending "save changes?" prompt, whether a quit is asking
ui.file	path; insert?: bool	starts an interactive background Open or Insert; poll ui.inspect.file_busy for completion; the window stays responsive
ui.home	open?: bool; sample?: index	the start page: show or hide it, open a built-in sample (once built); returns open and the recent designs
ui.shortcut	command, key?, replace?	a command's key, or rebinds it ("" clears; a key another command uses is refused unless replace)
ui.help	item?: about, shortcuts (read only), report (copies diagnostics), crashes (the Crash Reports window)	the version, commit, build date and diagnostic text
ui.prefs	any of default_units, nav (fusion, solidworks, inventor, alias, tinkercad, openscad), zoom_reverse, zoom_to_cursor, smooth_wheel_zoom (default true), trackpad_pan (default true: two-finger scroll pans, pinch zooms), orbit_cursor, look_at_anim, look_at_speed, msaa, length_decimals, angle_decimals, theme (dark, light, system), language (en, ja; see localization), ui_scale, up_axis (z, y), offer_stand_up; open (a page: General, Navigation, Keyboard Shortcuts, Design, Graphics, Sketch, Selection) opens the Preferences dialog there; button: ok, cancel, apply, defaults; stand_up: true stands up a just-opened Y-up file	sets preferences (kept between runs), returns them all plus dialog (the open page or null), dark and stand_up_offer
ui.capture	action?: capture, revert, cancel	answers the Capture Position question (asked when a command starts or the design is saved while components were moved without capturing); without action, what waits
ui.window	action: minimize, maximize, restore, toggle, close	what the title bar's caption buttons do (on Windows and Linux the application bar is the title bar); close asks about unsaved designs first
ui.agent_cursor	show (bool), speed: a number from 1 to 5 (times the normal speed) or "instant" (no animation: the command runs at once and the pointer jumps to where it acted), follow_camera (bool); all optional	the settings. While the cursor is shown, engine.execute first glides to the command's toolbar button and to each pick, then runs and replies; later requests wait their turn. "animate": false on a call skips it
ui.resize	width, height
app.quit	force? (quit without asking about unsaved designs)	quitting (the window closes), asking (a "save changes?" prompt is open)

MCP

solidcraft-cli mcp --connect 127.0.0.1:PORT bridges an MCP client (an AI agent) to this channel; see mcp.md.

Example

{"id":1,"method":"engine.execute","params":{"command":"sketch.create","params":{"plane":"XY"}}}
{"id":2,"method":"engine.execute","params":{"command":"sketch.rectangle.two_point","params":{"p0":[0,0],"p1":[40,30]}}}
{"id":3,"method":"engine.execute","params":{"command":"solid.extrude","params":{"distance":20}}}
{"id":4,"method":"engine.execute","params":{"command":"solid.fillet","params":{"edges":[[0,0,10]],"radius":3}}}
{"id":5,"method":"ui.screenshot","params":{"path":"/tmp/part.png"}}

Hold Shift during an orbit gesture to snap to the nearest standard or diagonal view. This applies to right-drag, the Orbit navigation tool, and dragging the axis view. Under the default preset, Shift+middle also orbits with snapping; middle alone pans. Axis-view tips use world coordinates, regardless of the up-axis preference. Clicking an aligned tip again flips to its opposite.

Shift-orbit snapping includes 45-degree edge views and isometric corner views, with a lightly damped spring transition and a small boundary margin to prevent flicker.