# US Code of Federal Regulations (pypi · cfr-mcp)

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

- Trust score: 80/100 (high trust)
- Change this week: +4
- Registry status: active
- Liveness: live
- Owner verified: no
- Last scored: 2026-09-21

## Components

- pypi · `cfr-mcp`: 80/100 (this document), [markdown](https://verifymcp.io/servers/mccallar-cfr-mcp/cfr-mcp.md), [page](https://verifymcp.io/servers/mccallar-cfr-mcp/cfr-mcp)

## Channel facts

- Registry: `pypi`
- Package: `cfr-mcp`
- Version: `0.2.2`
- Transport: `stdio`

## Trust breakdown

How this component scores in each security and reliability category. Every signal is checked automatically from public evidence about the published package, including repeated runs of it in an isolated sandbox, and we only credit what we can confirm. Scores are 0–100 per category. Scoring method: https://verifymcp.io/docs/scoring (what has changed: https://verifymcp.io/docs/scoring/changelog)

Scored 2026-09-21.

- **Supply Chain Security**: 100/100
  - No malware found by supply-chain analysis.
  - No known CVEs affecting this package version or its production dependencies.
  - Runs hatchling.build at install time, a recognised native-build step with no shell scripting around it.
  - 1 of 33 dependencies flagged as unhealthy.
- **Provenance & Transparency**: 48/100
  - Source repository is publicly reachable at the declared URL.
  - Provenance check failed: no build-provenance attestation is published.
  - Clear OSI-approved license (MIT).
  - Actively maintained (last published 22 days ago).
  - Publishes a security disclosure policy (SECURITY.md).
- **Schema Quality & AI Usability**: 71/100
  - AI-judged instruction clarity (good).
  - Tool/resource definitions use about 595 tokens (~85/item across 7 items; 7 tools + 0 resources), lean.
  - Usage-examples check failed: none of the tools include examples.
- **Stability & Change Management**: 77/100
  - Stability observed for 23 of 30 days with no destabilising changes; credit accrues until the full window elapses.
- **Tool Coverage**: 83/100
  - 100% of tools have a non-trivial description (not blank, and not just the tool's name).
  - 40% of tool parameters carry a description.
  - Structured output schemas are declared (100% of tools); any adoption earns full credit.
- **Tool Safety**: 100/100
  - No prompt-injection markers were found in the server instructions, tool names or descriptions we captured.
  - We read all 7 captured tool definition(s), and no name or description among them implies an irreversible operation.
  - An AI judge read all 8 captured unit(s) of tool text and found none that tries to manipulate the model reading it.
- **Capabilities**: 100/100
  - Implements a current MCP spec version (2026-07-28).

## Install

### How do I install the US Code of Federal Regulations MCP server?

US Code of Federal Regulations runs locally as a PyPI package, launched with uvx cfr-mcp. Ready-made configuration for Claude, Cursor, VS Code, Codex and 5 more is on this page, copied from each client's own documentation.

### Claude

```bash
claude mcp add mccallar-cfr-mcp -- uvx cfr-mcp
```

### Cursor

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

### VS Code

```json
{
  "servers": {
    "mccallar-cfr-mcp": {
      "command": "uvx",
      "args": [
        "cfr-mcp"
      ]
    }
  }
}
```

### Codex

```bash
codex mcp add mccallar-cfr-mcp -- uvx cfr-mcp
```

### opencode

```json
{
  "$schema": "https://opencode.ai/config.json",
  "mcp": {
    "mccallar-cfr-mcp": {
      "type": "local",
      "command": [
        "uvx",
        "cfr-mcp"
      ],
      "enabled": true
    }
  }
}
```

### OpenClaw

```bash
openclaw mcp add mccallar-cfr-mcp --command uvx --arg cfr-mcp
```

### Hermes

```yaml
mcp_servers:
  mccallar-cfr-mcp:
    command: "uvx"
    args: ["cfr-mcp"]
```

### Netclaw

```json
{
  "McpServers": {
    "mccallar-cfr-mcp": {
      "Transport": "stdio",
      "Command": "uvx",
      "Arguments": [
        "cfr-mcp"
      ]
    }
  }
}
```

### Vellum

```bash
assistant mcp add mccallar-cfr-mcp -t stdio -c uvx -a cfr-mcp
```

### Other

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

## Changelog

Every change recorded for this component, newest first. Days that predate change tracking, or that we cannot explain, say so: "we were watching and nothing happened" and "we were not watching" are different claims.

### 2026-09-21 (score 80, +1)

No change was recorded against any check on this day. Stability & Change Management went from 73 to 77. That category is still filling its 30-day observation window: 22 days of observed history at the previous scan, 23 at this one. The score rises as the window fills, whether or not the server changes.

### 2026-09-19 (score 79, +1)

No change was recorded against any check on this day. Stability & Change Management went from 67 to 70. That category is still filling its 30-day observation window: 20 days of observed history at the previous scan, 21 at this one. The score rises as the window fills, whether or not the server changes.

### 2026-09-17 (score 78, +1)

No change was recorded against any check on this day. Stability & Change Management went from 60 to 63. That category is still filling its 30-day observation window: 18 days of observed history at the previous scan, 19 at this one. The score rises as the window fills, whether or not the server changes.

### 2026-09-15 (score 77, +1)

No change was recorded against any check on this day. Stability & Change Management went from 53 to 57. That category is still filling its 30-day observation window: 16 days of observed history at the previous scan, 17 at this one. The score rises as the window fills, whether or not the server changes.

### 2026-09-12 (score 76, +1)

No change was recorded against any check on this day. Stability & Change Management went from 43 to 47. That category is still filling its 30-day observation window: 13 days of observed history at the previous scan, 14 at this one. The score rises as the window fills, whether or not the server changes.

### 2026-09-10 (score 75, +1)

No change was recorded against any check on this day. Stability & Change Management went from 37 to 40. That category is still filling its 30-day observation window: 11 days of observed history at the previous scan, 12 at this one. The score rises as the window fills, whether or not the server changes.

### 2026-09-08 (score 74, +1)

No change was recorded against any check on this day. Stability & Change Management went from 30 to 33. That category is still filling its 30-day observation window: 9 days of observed history at the previous scan, 10 at this one. The score rises as the window fills, whether or not the server changes.

### 2026-09-06 (score 73, +4)

- [functional improvement] Stability: unverified → 0.27

## MCP tools (7)

### `lookup_citation` (~106 tokens)

Retrieve the text of a specific CFR citation.

Large parts return an outline of their sections instead of full text;
follow up with a specific section citation to read it.

Input parameters:

- `citation` (string, required): e.g. '21 CFR 101.9', '40 CFR 261.4(b)(1)', '40 CFR Part 261 Subpart C'
- `date`: YYYY-MM-DD for point-in-time text. Omit for current.
- `max_chars` (integer)

Output parameters:

- `result` (string)

### `search_regulations` (~79 tokens)

Full-text search across the CFR.

Returns citations, headings and short snippets only — never full text.
Follow up with lookup_citation to read anything.

Input parameters:

- `agency`: Agency slug from list_agencies
- `date`
- `limit` (integer)
- `query` (string, required)
- `title`: Limit to a CFR title

Output parameters:

- `result` (string)

### `where_does_term_appear` (~71 tokens)

Show which titles/chapters/parts contain a term, with hit counts.

Cheap orientation tool: fetches no regulation text at all. Use this before
searching when you don't know which part of the CFR governs a topic.

Input parameters:

- `date`
- `query` (string, required)

Output parameters:

- `result` (string)

### `browse_structure` (~41 tokens)

Return the CFR hierarchy for a title (or one part) without any text.

Input parameters:

- `date`
- `part`
- `title` (integer, required)

Output parameters:

- `result` (string)

### `what_changed` (~77 tokens)

List amendment dates for a citation, plus any published corrections.

Each amendment is cross-linked to the Federal Register rule that caused
it, with a URL to the rulemaking (whose preamble explains the why).
Follow up with compare_versions to see exactly what text changed.

Input parameters:

- `citation` (string, required)
- `since`: YYYY-MM-DD

Output parameters:

- `result` (string)

### `compare_versions` (~148 tokens)

Show how a citation's text differs between two dates, as a diff.

Use what_changed first to find amendment dates worth comparing; pass the
day before an amendment as date_a and the amendment date as date_b to see
exactly what that rule changed. Both dates must be 2017-01-03 or later.

Input parameters:

- `citation` (string, required): A section citation like '40 CFR 261.4', optionally with a paragraph: '40 CFR 261.4(b)'
- `date_a` (string, required): Earlier date, YYYY-MM-DD
- `date_b`: Later date, YYYY-MM-DD. Omit for the current text.
- `max_chars` (integer)

Output parameters:

- `result` (string)

### `list_agencies` (~45 tokens)

List federal agencies and the CFR titles/chapters they administer.

Use this to turn a name like "EPA" into the right CFR title before searching.

Input parameters:

- `filter`

Output parameters:

- `result` (string)

## Diagnostics

Captured diagnostic sections: Provenance, Install scripts, Dependencies. The full working is on the page: https://verifymcp.io/servers/mccallar-cfr-mcp/cfr-mcp#diagnostics

## Score history

- 2026-09-21: 80
- 2026-09-20: 79
- 2026-09-19: 79
- 2026-09-18: 78
- 2026-09-17: 78
- 2026-09-16: 77
- 2026-09-15: 77
- 2026-09-14: 76
- 2026-09-13: 76
- 2026-09-12: 76
- 2026-09-11: 75
- 2026-09-10: 75
- 2026-09-09: 74
- 2026-09-08: 74
- 2026-09-07: 73
- 2026-09-06: 73
- 2026-09-05: 69
- 2026-09-04: 69
- 2026-09-03: 69
- 2026-09-02: 69
- 2026-09-01: 69
- 2026-08-31: 69
- 2026-08-30: 69
- 2026-08-29: 54

## Common questions

### What is the US Code of Federal Regulations MCP server?

US Code of Federal Regulations is an MCP server listed in the public MCP registry as io.github.mccallar/cfr-mcp. Look up, search, and track changes to the US Code of Federal Regulations (eCFR). This page covers its PyPI package (cfr-mcp).

### Is the US Code of Federal Regulations MCP server safe to use?

US Code of Federal Regulations scores 80 out of 100 on VerifyMCP. We found no known CVEs affecting it as of 21 September 2026. That is a record of what we were able to check automatically, not an endorsement. The category breakdown on this page shows every signal behind the number, including the ones we could not confirm.

### What tools does the US Code of Federal Regulations MCP server expose?

US Code of Federal Regulations exposes 7 tools: lookup_citation, search_regulations, where_does_term_appear, browse_structure, what_changed, and 2 more. Their descriptions and schemas cost roughly 567 tokens of context every time the server is loaded.

### Is the US Code of Federal Regulations MCP server still maintained?

US Code of Federal Regulations is still listed as active in the MCP registry. We last reached this channel on 21 September 2026. Those dates come from our own scans of the registry and the channel itself, not from anything the publisher announced.

### What licence is the US Code of Federal Regulations MCP server under?

US Code of Federal Regulations declares the MIT licence, which is OSI-approved. That covers the source only, and says nothing about the cost of any service it calls.

## Links

- PyPI project: https://pypi.org/project/cfr-mcp/
- Socket report: https://socket.dev/pypi/package/cfr-mcp
- Repository: https://github.com/mccallar/cfr-mcp
- Changelog RSS feed: https://verifymcp.io/servers/mccallar-cfr-mcp/cfr-mcp.xml
- Changelog JSON feed: https://verifymcp.io/servers/mccallar-cfr-mcp/cfr-mcp.json
- HTML version of this page: https://verifymcp.io/servers/mccallar-cfr-mcp/cfr-mcp