Show HN: An OSS text to CAD MCP and API

Developer Zesuperaker released scratchcad, an open-source Rust solid-modelling API and MCP server that lets AI assistants generate CAD geometry from text prompts, licensed under Apache License 2.0. The MCP server runs on Python 3.14 with FastMCP and exposes the service's five endpoints as tools over streamable HTTP at http://localhost:8000/mcp, supporting Claude Code, OpenAI Codex CLI, Gemini CLI and VS Code GitHub Copilot agent mode. The project is under active development, with APIs, tools and script syntax subject to change without notice.

Warning scratchcad is under active development. APIs, tools and script syntax may change without notice, and things may break between commits. scratchcad is a rust based solid modelling API, plus an MCP server so AI assistants can use it. docker compose up --build or docker compose watch to reload on edits Then add the MCP server http://localhost:8000/mcp to your agent: Claude Code claude mcp add --transport http scratchcad http://localhost:8000/mcp OpenAI Codex CLI codex mcp add scratchcad --url http://localhost:8000/mcp Gemini CLI gemini mcp add --transport http scratchcad http://localhost:8000/mcp VS Code GitHub Copilot agent mode code --add-mcp '{"name":"scratchcad","type":"http","url":"http://localhost:8000/mcp"}' For other clients, point them at http://localhost:8000/mcp using the streamable HTTP transport. | prompt using opus 5.5 medium through cc | output | |---|---| | Create an M10 hex bolt with 26 mm thread length, a course pitch of 1.5 mm and head height 6.4 mm. Also create a matching hex nut with 8.4 mm height. Both of these should be in the same file displayed beside each other. | | | Create a 3DBenchy. | | | Create a mid-stage compressor blisk with these dimensions: an outer tip diameter of 440 mm, a hub platform diameter of 241.2 mm, and a radial blade span of 99.4 mm across its 29 twisted aerodynamic airfoils. Mechanically, the component is defined by an 80.0 mm shaft interface bore diameter, an axial hub length of 77.5 mm, and an airfoil rim width of 45.0 mm, with rear mounting flange diameters measuring 184 mm at the inner shoulder and 202 mm at the outer rim. Blade count of 29 twisted aerodynamic airfoils. | | compose.yaml runs both dev images: | service | port | image | |---|---|---| | server | 127.0.0.1:8080 | server/Dockerfile.dev https://github.com/Zesuperaker/scratchcad/blob/main/server/Dockerfile.dev : cargo run with fast incremental rebuilds | | mcp | 127.0.0.1:8000 | mcp/Dockerfile.dev https://github.com/Zesuperaker/scratchcad/blob/main/mcp/Dockerfile.dev : the MCP server over streamable HTTP at /mcp | Run the MCP checks inside its container with docker compose run --rm mcp uv run pytest . With docker compose watch , edits under server/src or mcp/src restart the affected container the Rust side recompiles in a few seconds , and changes to Cargo.toml , Cargo.lock , pyproject.toml or uv.lock rebuild its image. To require an API token, put SCRATCHCAD API TOKEN=<16+ characters in a .env file next to compose.yaml . Exported STL files appear in ./output . These will be the main file that you recieve from the agent unless you also explicitly ask for the Rhai script that the agent created to be saved to ./output . | directory | what it is | |---|---| | server/ https://github.com/Zesuperaker/scratchcad/blob/main/server | The scratchcad HTTP service Rust 1.98, Fidget https://github.com/mkeeter/fidget + axum . Validates, evaluates, renders and meshes Rhai https://rhai.rs scripts that describe implicit surfaces. | | mcp/ https://github.com/Zesuperaker/scratchcad/blob/main/mcp | An MCP https://modelcontextprotocol.io server Python 3.14, FastMCP https://gofastmcp.com that exposes the service's five endpoints as tools, so a model can write a script, look at renders, measure the part and export an STL. | The two are independent: the MCP server talks to the service over HTTP, so it works with a local build, the dev containers, or a deployed instance. scratchcad is licensed under the Apache License 2.0 https://github.com/Zesuperaker/scratchcad/blob/main/LICENSE . Its dependencies, are listed with their licenses in THIRD PARTY LICENSES.txt https://github.com/Zesuperaker/scratchcad/blob/main/THIRD PARTY LICENSES.txt . A huge shoutout to Matt Keeter the developer of Fidget https://github.com/mkeeter/fidget , scratchcad uses fidget as the core implicit kernal and this project would not be possible without fidget.