forked from 1b-agent/opencadstudio-upstream
100 lines
5.3 KiB
Markdown
100 lines
5.3 KiB
Markdown
# OpenCADStudio MCP control
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Every native OpenCADStudio build contains the same MCP server as the editor. `OpenCADStudio --mcp` starts it over stdio, opens the desktop editor when needed, and exposes the live document without Python, a package manager, a sidecar service, or client-specific code.
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MCP lets an AI client inspect the open drawing, execute editor commands, and verify the result through a shared protocol. Install OpenCADStudio, then add a local MCP server in the client and set its command to:
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```sh
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OpenCADStudio --mcp
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```
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The client must start that command over standard input/output. If it asks for the executable and arguments separately, select the installed `OpenCADStudio` executable and enter `--mcp` as its only argument. The exact registration screen or configuration location belongs to the client. Once connected, the four tools below should appear in the client's MCP tool list.
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The server provides four tools:
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- `ocs_sessions` finds running editor sessions and opens OpenCADStudio when none exists.
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- `ocs_read` reads document state, command manifests, entities, layers, properties, kernel measurements and spatial relationships, history, events, and operation status.
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- `ocs_execute` performs one operation or a sequential batch against the real editor.
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- `ocs_capture` returns a bounded PNG of the drawing viewport or complete window.
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The normal flow is to call `ocs_sessions`, pass its returned `session_id` as `ocs_session_id` to the other tools, read the chosen session with `ocs_read`, then pass the returned document state into `ocs_execute`. For example, an undo request has this shape:
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```json
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{
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"ocs_session_id": "SESSION_FROM_OCS_SESSIONS",
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"request": {
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"op": "undo",
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"request_id": "undo-1",
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"document_id": 1,
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"revision": 12
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}
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}
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```
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To discover command syntax without reading application source, call `ocs_read` with `op: "commands"`. The unfiltered response lists commands and actions. Add `parameters: {"name": "PLINE"}` for a command's batch examples and interactive guidance.
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A complete command can be sent with `run`. Prompt answers are separated by spaces, points use `x,y` or `x,y,z`, and option answers use their displayed token:
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```json
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{
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"ocs_session_id": "SESSION_FROM_OCS_SESSIONS",
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"request": {
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"op": "run",
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"request_id": "polyline-1",
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"document_id": 1,
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"revision": 12,
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"cmd": "PLINE 0,0 10,0 10,10 C"
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}
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}
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```
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Use `batch` when the steps are already known. OCS supplies each step with the state produced by the previous one and stops on the first failure. `completed_steps` and `next_step` show exactly what committed:
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```json
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{
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"ocs_session_id": "SESSION_FROM_OCS_SESSIONS",
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"response_detail": "changed_entities",
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"request": {
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"op": "batch",
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"request_id": "shape-1",
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"steps": [
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{"op": "run", "cmd": "LINE 0,0 10,0"},
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{"op": "run", "cmd": "CIRCLE 5,5 2"}
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]
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}
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}
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```
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Execute responses use `response_detail: "compact"` by default and return only the state needed for the next edit. Use `changed_entities` to receive the current geometry of affected handles in the same response, or `full` when the complete editor state is needed.
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`ocs_read` query accepts exact handles, type/layer filters, field projection, world-XY bounds, nearest-curve ranking, closed-curve containment, and exact intersections between two planar curves. Nearest points, containment, curve length, area, and intersections are calculated by the geometry kernel:
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```json
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{
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"ocs_session_id": "SESSION_FROM_OCS_SESSIONS",
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"op": "query",
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"parameters": {"intersections": ["2A", "31"]}
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}
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```
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For unfamiliar or conditional commands, use `start`, then inspect `state.command` in every response. Its `accepts` array gives the valid MCP input kinds, `options` gives the current tokens, and `input_example` gives the next request shape. Add the current state fields and a new `request_id` to each step.
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Every `ocs_execute` request requires a caller-generated `request_id`. Reuse that ID only to retry the identical request after a timeout, together with the same session ID, document ID, expected revision, and selection. Commands report `waiting_input` while more input is required and asynchronous work remains `running` until its real callback finishes. Geometry stays in OpenCADStudio and its geometry kernel.
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`ocs_capture` defaults to the drawing viewport and a longest edge of 1600 pixels. Set `scope` to `window` for the full interface or change `max_dimension` between 256 and 4096.
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Clients using MCP 2026-07-28 can advertise `io.modelcontextprotocol/tasks`. OCS then returns a standard task handle when an operation is still running and accepts `tasks/get`, `tasks/update`, and `tasks/cancel`. Other clients continue to receive the existing operation status and can read it with `ocs_read`.
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The source-tree protocol smoke test treats the executable as a black box and uses only the Python standard library. It checks both supported protocol styles, the published schemas, structured errors, and the four-tool surface:
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```sh
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cargo build
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python3 docs/automation/mcp_smoke.py target/debug/OpenCADStudio
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```
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The repeatable live-editor evaluation draws three isolated entities in one batch, verifies exact intersections, nearest geometry and kernel measurements, removes the entities, and reports call count, elapsed time and wire bytes:
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```sh
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python3 docs/automation/mcp_eval.py target/debug/OpenCADStudio
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```
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