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US Code of Federal Regulations

Official registry Developer tools

Look up, search, and track changes to the US Code of Federal Regulations (eCFR).

Source code Documentation

Install

Add this to your client's MCP configuration (Claude Desktop: claude_desktop_config.json; Cursor: .cursor/mcp.json; VS Code and others use the same "mcpServers" shape).

PYPI package cfr-mcp
Claude Code 
claude mcp add us-code-of-federal-regulations -- uvx cfr-mcp==0.2.2
JSON configuration (Claude Desktop, Cursor, VS Code) 
{
    "mcpServers": {
        "us-code-of-federal-regulations": {
            "command": "uvx",
            "args": [
                "cfr-mcp==0.2.2"
            ]
        }
    }
}

Documentation

From the project's README on GitHub, refreshed weekly. Links open on GitHub.

Contents
  1. cfr-mcp
  2. Install
  3. Tools
  4. Design notes
  5. Legal
  6. Development

cfr-mcp

An MCP server that gives AI assistants access to the US Code of Federal Regulations.

Ask "what does 21 CFR 101.9 require?" or "has 40 CFR 261 changed since 2023?" and get the actual regulation text, with citations, instead of a plausible-sounding guess.

Unofficial community project. Not affiliated with or endorsed by the Office of the Federal Register, NARA, or GPO, and uses no government seals or logos.

Maintained by one person as a personal project and provided as-is (MIT). Issues and pull requests are welcome but may not get a quick response. To report a security issue, see SECURITY.md.

Install

Requires Python 3.11+. No API key — the eCFR and Federal Register APIs are open.

Claude Code:

claude mcp add cfr -- uvx cfr-mcp

Any other MCP client:

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

Tools

ToolWhat it does
lookup_citationText of a citation — 21 CFR 101.9, 40 CFR 261.4(b)(1), 40 CFR Part 261 Subpart C
search_regulationsFull-text search; returns citations and snippets, never bodies
where_does_term_appearWhich titles contain a term, with hit counts. Fetches no text
browse_structureThe hierarchy of a title or part, no text
what_changedAmendment history for a citation, linking each change to the Federal Register rule that caused it, plus published corrections
compare_versionsDiff of a citation's text between two dates — see exactly what an amendment changed
list_agenciesMaps agency names to the CFR titles they administer

Point-in-time works throughout: pass date as YYYY-MM-DD to read the CFR as it stood.

Design notes

Context budget is the whole game. The eCFR full endpoint returns an entire downloadable XML document for a title-level request. Every tool here caps output and degrades to an outline rather than dumping text into the model's context. Title-level XML requests are refused outright.

Dates must be resolved, not assumed. Versioner routes 404 on dates that aren't valid issue dates for a title, so the client resolves through titles.json first rather than passing today's date blindly.

Caching is courtesy. The eCFR publishes no rate limit and has no key to identify callers politely, so the client caches to disk (historical dates forever, since point-in-time content is immutable) and self-limits concurrency. The cache lives in ~/.cache/cfr-mcp (respects XDG_CACHE_HOME); set CFR_MCP_CACHE_DIR to relocate it.

Regulation text is free to reproduce. 1 CFR 2.6 states that any person may reproduce or republish material appearing in the Federal Register, with no restrictions on what is reproduced, who reproduces it, or where. Federal government works are also outside copyright under 17 U.S.C. §105.

Incorporation by reference. Some CFR sections incorporate private standards (ASTM, NFPA, ASHRAE) whose copyright status after incorporation remains unsettled. The eCFR does not contain the text of those standards and neither does this server — it returns the citation only. Obtain standards from the issuing organization or the Office of the Federal Register reading room.

Status of the text. The eCFR is authoritative but unofficial. Anyone relying on it for legal research should verify against the current official CFR, the daily Federal Register, and the List of CFR Sections Affected (LSA).

Not legal advice. This is a retrieval tool. It returns the text of regulations; it does not tell you whether you are compliant with them.

Development

uv sync --extra dev
uv run pytest

MIT licensed.

Frequently asked questions

What is US Code of Federal Regulations?

Look up, search, and track changes to the US Code of Federal Regulations (eCFR).

How do I install US Code of Federal Regulations?

It runs on your machine. In Claude Code: claude mcp add us-code-of-federal-regulations -- uvx cfr-mcp==0.2.2. For other clients, paste the JSON configuration from this page into their MCP settings.

Does US Code of Federal Regulations need an API key?

Its registry entry lists no required key or secret. Some features may still need an account with the service it connects to.

Is US Code of Federal Regulations open source?

Yes. Its code is on GitHub under the MIT license.

Who maintains US Code of Federal Regulations?

It is published by mccallar. AI.tn lists it but does not maintain or endorse it.

From the official MCP Registry. Listing is not an endorsement: review a server's code and permissions before giving it access to your data.