US Code of Federal Regulations

Name: US Code of Federal Regulations
Author: mccallar

by mccallarversion 0.2.2i★ –iRuns on your computer

Registry nameio.github.mccallar/cfr-mcp

Install

Overview

Description from the maker (original English)

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

PopNx MCP’s three pillars

These three are never merged into one score: opinions, measurements and popularity are different things.

User voiceiNo reviews yetReviews open together with accounts in a later step
Our basic checksi1 of 1 passedChecked from public information; code not scanned yet
UsageiNot measured yet★ –

What you can do with it

We have not written a plain-language summary for this one yet. Below are the facts we read from the registry.

Connection: Runs on your computer
Transport: stdio
Category: Search & AI memory

Install

Pick the AI app you use, then copy the settings.

Before you install

Basic checks: 1 of 1 passed
Runs on your computer with your user’s permissions (files, network, apps).
The registry lists no key to fill in.

You need

PyPIPython’s uv installed (for the uvx command)

Which app do you use?

ClaudeClaude CodeCursorVS CodeChatGPT

Pick your app above. We remember it, so next time the button says “Install in …”.

Open Claude Desktop → Settings → Developer → Edit Config, and paste this into claude_desktop_config.json

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

Run this in your terminal

claude mcp add cfr -- uvx cfr-mcp

Open in Cursor

Or copy the settings yourself

Paste into .cursor/mcp.json in your project, or ~/.cursor/mcp.json

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

Your browser asks to open the app, then the app shows the settings and asks you to confirm. Key values are left empty for you to fill in.

Open in VS Code

Or copy the settings yourself

Paste into .vscode/mcp.json in your project

{
  "servers": {
    "cfr": {
      "type": "stdio",
      "command": "uvx",
      "args": [
        "cfr-mcp"
      ]
    }
  }
}

Your browser asks to open the app, then the app shows the settings and asks you to confirm. Key values are left empty for you to fill in.

This one runs on your computer, and ChatGPT can only connect to servers on the internet. Pick another app.

Your choice stays on this device in a cookie; no account needed.

These settings are generated from the maker’s registry entry. If the README says otherwise, follow the README.

What it can do

Runs on your computer; the tool list appears in your AI app after you install it.

Basic checksi

We check information anyone can see; we have not read the code. Checks that do not apply are left out of the count. · Checked Nov 7, 2026

✓ Pass
Maker matches the repo
The registry name was verified with the GitHub account mccallar, which owns the repo
… Not checked yet
Still maintained
We have not read this repo from GitHub yet
… Not checked yet
Has a licence
We have not read this repo from GitHub yet
– Not applicable
Endpoint responds
This one runs on your computer; there is no internet endpoint
– Not applicable
Sign-in with OAuth
Runs on your computer and uses local settings instead
… Not checked yet
No hidden instructions in tool descriptions
Runs on your computer; we can only read tool lists from internet endpoints

Compared with others in Search & AI memoryi

More stars than 0% of the other 7274 servers in this category
Published to the registry more recently than 35% of the other 7274 servers in this category
Basic checks equal to or better than 100% of the other 7274 servers in this category

Compared with every active server in this category in the registry. Stars count only when the publisher owns the repo.

Common questions

Is US Code of Federal Regulations safe?

It passed 1 of 1 applicable basic checks. We have not read the code. Before adding a key or token, see what access the server asks for and use a key with only the permissions you need.

What keys or codes does it need?

The registry does not list a required key, though some servers ask you to sign in on first use.

Does it run on my computer or in the cloud?

It runs on your computer. Your AI app starts it when needed, and data does not pass through the maker’s servers (unless it calls an online service itself).

Is it still maintained?

The GitHub repo last changed –, and the latest version (0.2.2) reached the registry 2 months ago.

Which apps can use it?

Apps that support MCP, such as Claude Desktop, Claude Code, Cursor and VS Code. You also need Python (uv) on your computer.

What can I use instead?

In the same category: Context7, Codebase Memory, Exa

Alternatives

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Reading a card:★ GitHub starsiThree pillars: reviews · checks · usageiUpdated = latest version published to the registryi

Context7

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Codebase Memory

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Exa

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Connect AI agents to Exa for web search, content fetching, and multi-step research.

Runs in the cloud★ 5,213MITUpdated last month

Install

README from the maker

Open the README

Copied from the maker’s repo as written. PopNx MCP has not reviewed or endorsed it. HTML, images and scripts are removed. Links lead off this site.

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

Tool	What it does
`lookup_citation`	Text of a citation — `21 CFR 101.9`, `40 CFR 261.4(b)(1)`, `40 CFR Part 261 Subpart C`
`search_regulations`	Full-text search; returns citations and snippets, never bodies
`where_does_term_appear`	Which titles contain a term, with hit counts. Fetches no text
`browse_structure`	The hierarchy of a title or part, no text
`what_changed`	Amendment history for a citation, linking each change to the Federal Register rule that caused it, plus published corrections
`compare_versions`	Diff of a citation's text between two dates — see exactly what an amendment changed
`list_agencies`	Maps 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.

Legal

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.

US Code of Federal Regulations

Overview

PopNx MCP’s three pillars

What you can do with it

Install

Before you install

What it can do

Basic checksi

Maker matches the repo

Still maintained

Has a licence

Endpoint responds

Sign-in with OAuth

No hidden instructions in tool descriptions

Compared with others in Search & AI memoryi

Common questions

Alternatives

Context7

Codebase Memory

Exa

README from the maker

cfr-mcp

Install

Tools

Design notes

Legal

Development