Errorcatalog MCP Server

errorcatalog

Every error message thrown in a codebase, catalogued — and, when you supply the documentation, a note of whether each message is documented.

errorcatalog scans source text line by line for throw statements of the form throw new <Name>Error(...), where the type name ends in Error (Error, TypeError, RangeError, or a custom type such as FooError). For each throw site it records the file, the 1-based line, the error type, and:

• literal — the first argument is a double-quoted, single-quoted, or backtick string with no ${ in it. The message is recorded exactly as written, escape sequences included — nothing is unescaped.
• dynamic — the first argument is anything else: a template containing ${, an identifier, a call, a concatenation, or a literal that does not close on the same line. The message is null.
• no message — throw new <Name>Error() with no argument at all. The message is null and the entry carries the note no message argument.

Throws that are not new <Name>Error(...) — a bare string, a non-Error constructor, a variable — are not catalogued. Duplicate throws stay as separate entries: the catalog is per throw site.

When documentation texts are supplied, each literal message is checked verbatim against them: documented is true when the message appears as a substring of some supplied doc, false when it does not, and null for dynamic and no-message entries — and for every entry when no docs are supplied, in which case the result reports docs_provided: false and the documented / undocumented counts are both 0.

Known limitation, by design: only the first line of a throw statement is inspected, so a literal whose argument list spans lines is catalogued as dynamic. The analysis is pure local text work: no network, no filesystem access in the core.

CLI

npx @reneturcios/errorcatalog catalog --sources sources.json --docs docs.json
npx @reneturcios/errorcatalog --version

sources.json and docs.json each contain a JSON array of {"path": "src/app.ts", "content": "..."} objects. The --docs flag is optional. The catalog is printed as JSON.

Exit codes: 0 on success, 1 on a runtime error (including an unreadable or invalid JSON file, or a malformed entry — the error names the offending path, e.g. sources[0].content is required), 2 on a usage error.

MCP server

npx -y @reneturcios/errorcatalog mcp

MCP client config:

{
  "mcpServers": {
    "errorcatalog": {
      "command": "npx",
      "args": ["-y", "@reneturcios/errorcatalog", "mcp"]
    }
  }
}

Tools

• catalog_errors — Catalogue every error thrown in the given sources, and whether each literal message is documented.

  • sources (array, required, at least 1) — source files as {path, content} objects
  • docs (array, optional) — documentation texts as {path, content} objects; literal messages are checked verbatim against them

  Returns {errors, counts, docs_provided}, where each error is {path, line, error_type, message, dynamic, documented} (plus note on no-message entries) and counts is {total, literal, dynamic, no_message, documented, undocumented}.

Docker

docker run -i ghcr.io/cloudcorprecords/errorcatalog
docker run --rm -v "$PWD:/w" ghcr.io/cloudcorprecords/errorcatalog catalog --sources /w/sources.json

Development

npm install
npm run build   # tsc -> dist/
npm test        # tsx --test test/*.test.ts (pure local, no network)
npm run dev     # run the CLI from source

License

MIT — Copyright (c) 2026 Rene Turcios