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scratchcad
[!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.
Quick start (requires docker)
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.
Examples
| 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. |  |
Docker info
compose.yaml runs both dev images:
| service | port | image |
|---|---|---|
server | 127.0.0.1:8080 | server/Dockerfile.dev: cargo run with fast incremental rebuilds |
mcp | 127.0.0.1:8000 | 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.
STL outputs
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.
Architecture
| directory | what it is |
|---|---|
server/ | The scratchcad HTTP service (Rust 1.98, Fidget + axum). Validates, evaluates, renders and meshes Rhai scripts that describe implicit surfaces. |
mcp/ | An MCP server (Python 3.14, FastMCP) 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.
License
scratchcad is licensed under the Apache License 2.0. Its dependencies, are listed
with their licenses in THIRD_PARTY_LICENSES.txt.
Shoutout
A huge shoutout to Matt Keeter the developer of Fidget, scratchcad uses fidget as the core implicit kernal and this project would not be possible without fidget.
Similar repos
Languages
Rust
61.1%
Python
38.0%
See what people are saying
README
scratchcad
[!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.
Quick start (requires docker)
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.
Examples
| 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. | |
Docker info
compose.yaml runs both dev images:
| service | port | image |
|---|---|---|
server | 127.0.0.1:8080 | server/Dockerfile.dev: cargo run with fast incremental rebuilds |
mcp | 127.0.0.1:8000 | 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.
STL outputs
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.
Architecture
| directory | what it is |
|---|---|
server/ | The scratchcad HTTP service (Rust 1.98, Fidget + axum). Validates, evaluates, renders and meshes Rhai scripts that describe implicit surfaces. |
mcp/ | An MCP server (Python 3.14, FastMCP) 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.
License
scratchcad is licensed under the Apache License 2.0. Its dependencies, are listed
with their licenses in THIRD_PARTY_LICENSES.txt.
Shoutout
A huge shoutout to Matt Keeter the developer of Fidget, scratchcad uses fidget as the core implicit kernal and this project would not be possible without fidget.
Similar repos
Languages
Rust
61.1%
Python
38.0%