A Model Context Protocol server over stdio: a CAD file, 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

cadmpeg answers "what is in this file, and can I have it as something else?" and this server exposes that:

• what can this build do? — cadmpeg_formats: the formats it reads and the formats it writes;
• what is in this file, and how faithfully was it read? — cadmpeg_inspect: the document and its decode report, which is where the losses are;
• give me another format — cadmpeg_convert: write the document out as STEP or as its own JSON.

Documents are opened once

Calls name a path; the server keeps the opened document, so a second question about the same file does not read it again. 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.