ecfr-mcp

MCP server for the eCFR (Electronic Code of Federal Regulations) API. Read FAR, DFARS, and all agency FAR supplement text with no authentication required.

Works with any MCP-compatible client (Claude Desktop, Claude Code, Cursor, Cline, Continue, Zed, etc.).

Tested and hardened through five rounds of integration testing against the live eCFR API. 101 regression tests covering 2 P0 catastrophic bugs, 26 P1 silent-wrong-data bugs, and 32 P2 validation gaps fixed. See TESTING.md for the full testing record.

What it does

Exposes the eCFR API as 13 MCP tools covering regulatory text, structure, search, version history, and common acquisition workflows:

Core endpoints

• get_latest_date - Get the most recent available date for a CFR title (call before other tools)
• get_cfr_content - Get parsed regulatory text for a section, subpart, or part
• get_cfr_structure - Hierarchical table of contents
• get_version_history - Amendment history for a section or part
• get_ancestry - Breadcrumb hierarchy path
• search_cfr - Full-text search with hierarchy filters
• list_agencies - All agencies with their CFR references
• get_corrections - Editorial corrections for a title

Workflow convenience

• lookup_far_clause - One-call FAR/DFARS clause text lookup (auto-resolves date)
• compare_versions - Side-by-side text comparison at two dates
• list_sections_in_part - All sections in a FAR/DFARS part
• find_far_definition - Search FAR 2.101 for a term definition
• find_recent_changes - Sections modified since a given date

No authentication required

The eCFR API is fully public. No API key, no registration, no auth headers. Just install and use.

Installation

Via uvx (recommended)

uvx ecfr-mcp

Via pip

pip install ecfr-mcp

From source

git clone https://github.com/1102tools/ecfr-mcp.git
cd ecfr-mcp
pip install -e .

Claude Desktop configuration

Add to ~/Library/Application Support/Claude/claude_desktop_config.json:

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

Restart Claude Desktop. The ecfr server appears in your MCP tools panel with 13 tools.

Example prompts

• "Pull the current text of FAR 15.305 (Proposal Evaluation) and summarize what it requires."
• "List all sections in FAR Part 19 (Small Business Programs)."
• "Look up the FAR definition of 'commercial product' in 2.101."
• "What FAR sections were amended in the last 6 months?"
• "Compare FAR 52.212-4 between 2024-01-01 and 2025-01-01 and show me what changed."
• "Get the current text of DFARS 252.227-7014 (Rights in Noncommercial Computer Software)."
• "Search Title 48 for 'organizational conflict of interest' and show me the relevant sections."
• "Which agency owns Chapter 8 in Title 48? Get their FAR supplement structure."

Design notes

• XML parsed server-side. The eCFR content endpoint returns raw XML. This server parses it into clean text (headings, paragraphs, citations) before returning to Claude, saving significant context tokens.
• Automatic date resolution. eCFR lags 1-2 business days behind the Federal Register. Using today's date on versioner endpoints causes 404 errors. All content tools auto-resolve to the latest available date unless you specify one.
• Search defaults to current text. Without date=current, eCFR search returns ALL historical versions including superseded. Default current_only=True prevents duplicate results.
• Structure endpoint limitation. The eCFR structure endpoint does not support section-level filtering (returns 400). list_sections_in_part works around this by fetching the part structure and walking the tree.
• FAR 2.101 optimization. The definitions section is ~109KB of XML. find_far_definition parses the full section server-side and returns only matching paragraphs with context.

CFR Title 48 quick reference

Chapter	Regulation	Parts
1	FAR	1-99
2	DFARS	200-299
3	HHSAR	300-399
4	AGAR	400-499
5	GSAR	500-599
6	DOSAR	600-699
7	AIDAR	700-799
8	VAAR	800-899
9	DEAR	900-999
18	NFS	1800-1899

Data source

All data from ecfr.gov, the continuously updated online Code of Federal Regulations maintained by the Office of the Federal Register. Updated daily, typically 1-2 business days after Federal Register publication. Not an official legal edition; for official citations reference the annual CFR from GPO.

Companion skill

This MCP mirrors the ecfr-api skill from 1102tools.com. The skill is markdown-based for interactive Claude use; the MCP wraps the same API as deterministic tool calls for agent workflows and automation.

License

MIT