RFC lookup

mcp-server-rfc

An MCP server that reads the RFC corpus with 40x fewer tokens and flags obsoleted specs.

{

"mcpServers": { "rfc": { "command": "uvx", "args": ["mcp-server-rfc"] } } }

No clone, no virtualenv, no path. That is the whole installation. Your client spawns the server on your machine and talks to it over stdin and stdout.

A client showing the server as connected has not necessarily used it, and a model will happily answer an RFC question from memory instead. On Claude Desktop the per-server log records only the handshake, so it cannot tell you either way — docs/desktop-verification.md says where the evidence actually is.

Tools

With the section index, a full-text query is words, and each result is one section ranked by BM25, carrying the section number to pass to get_rfc and the line that best matches. Without it, full-text search falls back to rg or grep over a synced mirror, where the query is a literal string and results are whole RFCs; regex=true opts into pattern matching there and in titles. The payload names the backend in tool. Title results put current RFCs before superseded ones, so a page cut short at limit keeps the document you want rather than the one it replaced.

get_rfc refuses any read of more than 1500 lines that is not a named section, answering with its size and a pointer to list_sections rather than filling the context with a specification the model had one question about; a start_line of 1 does not get around it. full=true overrides it. A section you asked for by name is never refused: list_sections reports how long each one is, and max_lines caps any read, so the choice is informed rather than blocked.

Every response carries a banner with the RFC's status and, when it applies, a warning that it has been superseded:

RFC 2616 — Hypertext Transfer Protocol -- HTTP/1.1  [DRAFT STANDARD]

!! OBSOLETED BY: RFC 7230, 7231, 7232, 7233, 7234, 7235

That warning is the reason to use this rather than let a model fetch rfc-editor.org itself. Models cite dead specifications with great confidence.

Full-text search

Works with no setup, fetching documents on demand. Full-text search additionally needs the section index, which the user downloads from a shell:

uvx mcp-server-rfc sync --index

About 270 MB from this project's GitHub releases, checked against its published SHA-256. It ranks sections by BM25 and serves every read from disk, so the server stops fetching from the RFC Editor. uvx mcp-server-rfc sync instead copies the corpus as 512 MB of text files from the RFC Editor's volunteer-run rsync mirror, which is what rg and regex=true search.

The same command that runs the server runs its CLI: sync downloads, status reports what is present, and uvx mcp-server-rfc --help covers the rest. It is also the command the server names in the error you get when full-text search is asked for without either.

Both are optional. The server deliberately does not expose a sync tool: hundreds of megabytes on someone's disk should be a person's decision, not a model's.

If an index or a mirror already exists — synced for the companion skill, say — this server picks it up automatically. It looks under the platform's data directory: $XDG_DATA_HOME/rfc-ai-tooling, or %LOCALAPPDATA%\rfc-ai-tooling on Windows, falling back to ~/.local/share/rfc-ai-tooling. Set $RFC_MIRROR to point at a non-default location — in a container with no home directory, that or --mirror is what to pass.

In a container, uvx on the host would write to the wrong disk. Keep the mirror in a named volume, fill it through the image, and set $RFC_CLI so the server's errors name that command instead of uvx mcp-server-rfc:

docker build -t mcp-server-rfc mcp/

docker run --rm -it -v rfc-mirror:/mirror mcp-server-rfc mcp-server-rfc sync --index docker run --rm -i -v rfc-mirror:/mirror -e RFC_TRANSPORT=stdio \ -e RFC_CLI="docker run --rm -it -v rfc-mirror:/mirror mcp-server-rfc mcp-server-rfc" \ mcp-server-rfc

HTTP mode

The config above is the stdio transport, which needs a client that can spawn a process on your machine. A session running in the cloud — claude.ai on the web, Cowork — cannot, and no configuration fixes that. For those, the server has to be deployed somewhere they can reach:

mcp-server-rfc --transport http --host 0.0.0.0 --port 8080

RFC_TRANSPORT, HOST and PORT are read from the environment too. The repository carries a Dockerfile and a fly.toml that do this. No public instance of this server exists and none is planned — if you want one, you host it, and you should put authentication in front of it, since the server has none and would otherwise be an open proxy to a volunteer-run mirror.

Full-text search works hosted only where the section index is on the server's disk (sync --index there). Without it, a hosted instance returns an error saying so instead of silently answering a title search. The obsolescence banner, section reads and the unscoped-read guard work either way, because they need only the 2 MB RFC index.

If your client has a shell

Use the skill instead — Claude Code, Codex CLI, OpenClaw, Cursor and Zed all qualify. It does the same things with fewer moving parts and gives the agent ripgrep over the corpus:

npx skills add shbernal/rfc-ai-tooling      # from the repo, into .claude/skills/

clawhub install @shbernal/rfc-lookup # or the last released version

This server is for clients that give the model no shell of its own. Claude Desktop is the clearest case: its chat cannot run a command on your machine, but it will spawn this server there.

Source, issues and the skill: https://github.com/shbernal/rfc-ai-tooling

MIT.