mcp-server-rfc

An MCP server for looking up IETF RFCs.

{
  "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

Queries are literal by default; regex=true opts into pattern matching, and under scope='fulltext' the dialect is whichever of rg or grep the machine has, which the payload names 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 Title results put current RFCs before superseded ones, so a page cut short at limit keeps the document you want rather than the one it replaced.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Every response carries a banner with the RFC's status and, when it applies, a warning that it has been superseded: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 requires a local mirror, which the user creates from a shell:

uvx mcp-server-rfc sync

The same command that runs the server runs its CLI: sync downloads the corpus, status reports what is present, and uvx mcp-server-rfc <command> --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 a mirror.

512 MB, a few minutes, entirely optional. The server deliberately does not expose a sync tool: half a gigabyte pulled from a volunteer-run mirror should be a person's decision, not a model's.

If 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.

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 is the one thing that does not survive: it reads a local 512 MB corpus, so 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 all work, because they need only the 2 MB 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.