A Model Context Protocol server over stdio: a STEP part, for an assistant.

One JSON-RPC message per line in, one out — the stdio transport, which is what a client launches as a process. No sessions, no server-sent events, no batches: every request is self-contained, which is what lets a client treat it as a pipe.

What the tools are for

quiddity answers "what is this part?" and this server exposes that, plus the geometry underneath it. The questions worth asking are different enough to be separate tools:

• what is it? — quiddity_part, quiddity_features, quiddity_face;
• what is here? — quiddity_probe and quiddity_sense: a ray, a point, and a camera frame rendered against the exact B-rep;
• how do two parts differ? — quiddity_correspond matches the features of one part against another's by name and size.

quiddity_export_mjcf is the one tool that writes: it puts the part on disk as a MuJoCo model.

Parts are opened once

Calls name a path; the server keeps the parsed part, so a second question about the same file does not re-read it. The cache is this process's — restarting the server costs a re-read, and nothing on disk depends on it.

A tool that cannot answer answers: a refusal is text saying what was wrong and what to try, never a dropped connection.