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US administrative law is where agencies turn statutes into binding rules — and it spans three official sources that don't talk to each other. This server stitches them into one workflow: the Federal Register (the daily journal of proposed/final rules and notices), the eCFR (the codified Code of Federal Regulations, full text, point-in-time), and Regulations.gov (rulemaking dockets and the public comments filed on them). Every Federal Register document carries the docket ID and CFR-part handles that chain across sources, so a rule can be traced proposal → comments → final → codified text in one sequence.

The agent sees regulatory verbs — search_rules, get_cfr_section, find_comments — not three API clients. The Federal Register and eCFR tools are keyless; the two Regulations.gov tools need a free api.data.gov key and return an actionable error without it.

Tools

Seven tools across the regulatory workflow. The Federal Register and eCFR tools (1–4, 7) are keyless. The two Regulations.gov tools (5–6) need REGULATIONS_GOV_API_KEY; regulations_list_open_comments runs keyless and only adds comment counts when the key is present.

Tool	Source	Key	Description
regulations_search_rules	Federal Register	—	Search proposed rules, final rules, notices, and presidential documents by query, type, agency, date range, and open-for-comment status. The primary discovery entry point.
regulations_get_document	Federal Register	—	Fetch one FR document by number — full metadata plus the cross-source handles (docket ID, CFR parts, comment count) that chain into the comment and codified-text tools.
regulations_browse_cfr	eCFR	—	Walk the CFR hierarchy (structure mode) or full-text-search the codified CFR (search mode). Both feed regulations_get_cfr_section.
regulations_get_cfr_section	eCFR	—	Read the codified text at a CFR location — a section, a whole part, or an appendix — current or as of a past date.
regulations_get_docket	Regulations.gov	✔	Pull a rulemaking docket and the documents filed in it (NPRM, final rule, supporting materials).
regulations_find_comments	Regulations.gov	✔	Fetch public comments on a document or docket, or one comment's full body and attachments. Flags attachment-only submissions.
regulations_list_open_comments	Federal Register (+ Reg.gov enrich)	optional	Rules currently open for public comment, closing soonest first. Fully functional keyless; enriches comment counts when keyed.

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regulations_search_rules

Search the Federal Register — the daily journal of US proposed rules, final rules, notices, and presidential documents (1994–present). Keyless.

• Full-text query across title and body, or browse by filters alone
• Filter by document type (PRORULE, RULE, NOTICE, PRESDOCU), agencies (Federal Register agency slug), and publication date window (published_after / published_before)
• Each result carries the documentNumber, docketIds, regulationIdNumbers (RIN), and cfrReferences that chain into the document, comment, and codified-text tools
• Pagination up to 100 per page, 50 pages; the Federal Register caps navigation at 5,000 records and the match count at 10,000 — when a result set is larger, the tool flags it and steers you to date-windowing

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regulations_get_document

Fetch one Federal Register document by its FR number — the stitching tool of this server. Keyless.

• Full metadata: title, type, agencies, abstract, action, effective/comment dates, RINs
• The output renders a cross-source handles block — the docket ID (→ regulations_get_docket / regulations_find_comments), affected CFR parts (→ regulations_get_cfr_section), and Regulations.gov document ID and comment count — each next to the tool name that consumes it
• include_full_text inlines the document body as plain text; default false returns the body URLs only (final rules can run tens of thousands of words)

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regulations_browse_cfr

Explore the codified Code of Federal Regulations via eCFR in two modes. Keyless.

• structure mode walks the CFR tree (all 50 titles, or one title's chapters → parts → sections) to discover a cite when the exact citation is unknown
• search mode runs a full-text query across the codified CFR and returns matching sections with their hierarchy path and a snippet
• title and part scope both modes, so a part surfaced by structure can be searched directly instead of filtering a whole title's hits by eye. A part needs its title in either mode — part numbers repeat across the Code — and is matched exactly, so pass it as eCFR writes it (58, not Part 58 or 058)
• A live search hit's hierarchyPath names the part it sits in (Part 51 — Requirements for Preparation, Adoption, and Submittal of Implementation Plans), so the subject matter is readable without a second call; a mirror hit's path stays structural, because the index stores no level names
• Search is served from the synced local mirror (FTS5) only when the mirror's title coverage can answer the request — a title it does not hold, an all-titles query against a scoped mirror, a date, or a cold deploy all go to the live eCFR search API instead
• Every search result reports source (mirror or live) and sourceScope — which corpus answered and what it covers, so an empty result is never mistaken for "no such regulation"
• date searches the section text in effect that day; eCFR indexes 2017-01-03 onward, and an undated search is pinned to eCFR's current index date rather than spanning every historical version
• Both modes assemble a cfrCite that feeds regulations_get_cfr_section, and both hand appendices back the same way: an appendix field with eCFR's verbatim identifier, and a cite that names the appendix rather than the part around it
• The mirror indexes section text only, so it never matches an appendix — its sourceScope says so, since otherwise an appendix that exists and one that does not both read as zero matches

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regulations_get_cfr_section

Read the codified text at a CFR location — one section, a whole part, or one appendix — via eCFR. Keyless.

• Answers "what does 40 CFR 50.1 say today?" and "...as of 2019-01-01?" — pass date for point-in-time text
• Provide title + part + section for one section, or omit section to fetch the whole part
• Provide appendix to read an appendix, passing the identifier verbatim as regulations_browse_cfr emits it (Appendix A-1 to Part 50, Schedule I to Part 789, Special Federal Aviation Regulation No. 88) — the identifiers are prose, not letters, and a short form matches nothing
• A whole-part read names the part's appendices and their headings but does not inline their text; appendices routinely run several times the length of the sections around them, so reading one is a deliberate second call
• Current single-section reads are served from the local mirror when ready (the source is reported); historical dates, whole-part fetches, appendix reads, and a cold mirror fall back to the live eCFR versioner
• The text carries what the XML carries: paragraphs, subheadings, editorial notes, tables (one pipe-delimited line per row), figure references, and the trailing source citation — the bracketed Federal Register history ([36 FR 22384, Nov. 25, 1971, as amended at 81 FR 68276, Oct. 3, 2016]) that leads back to the rulemakings behind the text
• A cite that names nothing returns the tool's not-found error with a recovery hint pointing at regulations_browse_cfr structure mode, not a bare upstream status
• eCFR retains historical versions back to roughly 2017; a date before coverage is rejected with guidance

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regulations_get_docket · key required

Pull a rulemaking docket from Regulations.gov by docket ID (e.g. EPA-HQ-OAR-2025-0194). Requires REGULATIONS_GOV_API_KEY.

• Docket metadata (title, agency, RIN, abstract) plus the documents filed in it (NPRM, final rule, supporting materials)
• Each returned document's objectId feeds regulations_find_comments(document_object_id); frDocNum chains back to regulations_get_document
• A docket often holds hundreds of supporting materials — filter document_types to Proposed Rule / Rule to find the rule documents themselves
• An unknown docket ID returns the tool's not-found error with a recovery hint, not a raw upstream status
• Regulations.gov requires a page size of 5–250 and caps a query at 20 pages (5,000 records)

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regulations_find_comments · key required

Fetch public comments — the unique corpus of what citizens and organizations actually submitted. Requires REGULATIONS_GOV_API_KEY.

• Target with exactly one of: docket_id (all comments in a docket), document_object_id (comments on one document), fr_document_number (convenience — resolves the FR number to its Regulations.gov document internally), or comment_id (one comment's full detail). Supplying two is rejected with an actionable error rather than resolved by precedence
• An ID Regulations.gov cannot resolve comes back as the tool's not-found error with a recovery hint, whether the API reports it as a 404 or as the 400 it uses for an ID it cannot parse
• The list endpoint returns no body text or attachment info — call with comment_id to read a comment's body
• When a comment's real content is a PDF/DOCX attachment, the body is a stub and attachmentOnly is true; the attachment download URLs are returned so the agent knows where the substance lives. The flag reaches both the structured output and the rendered text
• Regulations.gov caps a query at 20 pages (5,000 records); a high-volume docket surfaces a sample, flagged as truncated

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regulations_list_open_comments

Rules currently open for public comment, sorted by closing date (soonest first) — "what can I still weigh in on?" Keyless, degrades gracefully.

• Filter by agencies (Federal Register slug) and query; closing_before finds deadlines you need to act on soon
• Each row carries daysRemaining, the documentNumber (→ regulations_get_document), and docketIds (→ regulations_find_comments)
• Fully functional without a key; when REGULATIONS_GOV_API_KEY is configured, each row is enriched with the comment count read from the Federal Register document's own embedded Regulations.gov info (no extra rate-limited call)

Resources

Type	Name	Description
Resource	regulations://document/{documentNumber}	A single Federal Register document — metadata plus cross-source handles (mirrors regulations_get_document, full text omitted).
Resource	regulations://cfr/{title}/{part}/{section}	Codified text of a current CFR section (mirrors regulations_get_cfr_section at the current date, mirror-backed with a live eCFR fallback).

All resource data is also reachable via the tool surface — tool-only MCP clients lose nothing. Collections (rule search, comment lists) are not exposed as resources; use regulations_search_rules and regulations_find_comments instead.

Features

Built on @cyanheads/mcp-ts-core:

• Declarative tool and resource definitions — single file per primitive, framework handles registration and validation
• Unified error handling — handlers throw, framework catches, classifies, and formats; typed error contracts with recovery hints
• Pluggable auth: none, jwt, oauth
• Swappable storage backends: in-memory, filesystem, Supabase, Cloudflare KV/R2/D1
• Structured logging with optional OpenTelemetry tracing
• STDIO and Streamable HTTP transports

Federal-regulations-specific:

• One workflow over three official sources — the agent sees regulatory verbs, not three API clients; which source is hit is a service-layer detail
• Cross-source stitching — every Federal Register document surfaces its docket ID and CFR-part handles next to the tools that consume them, priming the proposal → comments → final → codified-text trace
• Keyless core — Federal Register + eCFR (5 of 7 tools) is a complete deployment with no API key; the Regulations.gov leg layers on top
• Locally mirrored codified CFR — the eCFR is synced once into embedded SQLite + FTS5 and queried by exact cite or full text, with a live-API fallback whenever the mirror's title coverage cannot answer the request
• Three independent service clients, each with its own base URL, retry/backoff, and rate-limit handling (Regulations.gov honors Retry-After on 429)

Agent-friendly output:

• Provenance on every CFR read — source: "mirror" | "live" so agents know whether text came from the synced index or the live API, and on search a sourceScope line naming what that corpus covers
• Honest truncation — Federal Register (50-page / 5,000-record) and Regulations.gov (20-page / 5,000-record) ceilings are surfaced with guidance to narrow, never silently dropped
• Attachment-aware comments — attachmentOnly flags when a comment's substance is a file rather than inline text, with the download URLs, on both the structured and text surfaces
• Actionable auth_required errors — the two keyed tools name the env var and the free signup URL rather than passing through a raw 401/403

Getting started

Public Hosted Instance

A public instance is available at https://federal-regulations.caseyjhand.com/mcp — no installation required. Point any MCP client at it via Streamable HTTP:

{
  "mcpServers": {
    "federal-regulations-mcp-server": {
      "type": "streamable-http",
      "url": "https://federal-regulations.caseyjhand.com/mcp"
    }
  }
}

Self-Hosted / Local

Add the following to your MCP client configuration file. The Federal Register and eCFR tools work with no key; set REGULATIONS_GOV_API_KEY (free at api.data.gov/signup) to enable the Regulations.gov docket and comment tools.

{
  "mcpServers": {
    "federal-regulations-mcp-server": {
      "type": "stdio",
      "command": "bunx",
      "args": ["@cyanheads/federal-regulations-mcp-server@latest"],
      "env": {
        "MCP_TRANSPORT_TYPE": "stdio",
        "MCP_LOG_LEVEL": "info",
        "REGULATIONS_GOV_API_KEY": "your-key-here"
      }
    }
  }
}

Or with npx (no Bun required):

{
  "mcpServers": {
    "federal-regulations-mcp-server": {
      "type": "stdio",
      "command": "npx",
      "args": ["-y", "@cyanheads/federal-regulations-mcp-server@latest"],
      "env": {
        "MCP_TRANSPORT_TYPE": "stdio",
        "MCP_LOG_LEVEL": "info",
        "REGULATIONS_GOV_API_KEY": "your-key-here"
      }
    }
  }
}

Or with Docker:

{
  "mcpServers": {
    "federal-regulations-mcp-server": {
      "type": "stdio",
      "command": "docker",
      "args": [
        "run", "-i", "--rm",
        "-e", "MCP_TRANSPORT_TYPE=stdio",
        "-e", "REGULATIONS_GOV_API_KEY=your-key-here",
        "ghcr.io/cyanheads/federal-regulations-mcp-server:latest"
      ]
    }
  }
}

Omit the REGULATIONS_GOV_API_KEY line entirely to run the keyless core (Federal Register + eCFR). The two Regulations.gov tools then return an actionable auth_required error, and regulations_list_open_comments runs without comment counts.

For Streamable HTTP, set the transport and start the server:

MCP_TRANSPORT_TYPE=http MCP_HTTP_PORT=3010 bun run start:http
# Server listens at http://localhost:3010/mcp

Prerequisites

• Bun v1.3 or higher (or Node.js v24+).
• Optional: a free api.data.gov key for the Regulations.gov tools (regulations_get_docket, regulations_find_comments, and comment counts in regulations_list_open_comments). The Federal Register and eCFR tools need no key. The shared key allows 1,000 requests/hour.

Installation

1. Clone the repository:

git clone https://github.com/cyanheads/federal-regulations-mcp-server.git

2. Navigate into the directory:

cd federal-regulations-mcp-server

3. Install dependencies:

bun install

4. Configure environment:

cp .env.example .env
# optionally set REGULATIONS_GOV_API_KEY

Configuration

All configuration is validated at startup via Zod schemas in src/config/server-config.ts. Key environment variables:

Variable	Description	Default
REGULATIONS_GOV_API_KEY	api.data.gov key for the Regulations.gov tools (get_docket, find_comments, and comment-count enrichment in list_open_comments). Optional — the Federal Register and eCFR tools work without it.	—
FEDERAL_REGISTER_BASE_URL	Federal Register API v1 base URL.	https://www.federalregister.gov/api/v1
ECFR_BASE_URL	eCFR API base URL.	https://www.ecfr.gov/api
REGULATIONS_GOV_BASE_URL	Regulations.gov API v4 base URL.	https://api.regulations.gov/v4
ECFR_MIRROR_PATH	Filesystem path for the eCFR SQLite mirror database.	./data/ecfr-mirror.sqlite
ECFR_MIRROR_REFRESH_CRON	Cron expression for the weekly mirror refresh (HTTP transport only).	0 4 * * 0
ECFR_MIRROR_TITLES	Comma-separated CFR title numbers to scope the mirror to (e.g. 21,40). Omit to mirror all 50 titles. Cites and searches outside the set fall through to the live eCFR API, as does any all-titles search while this is set.	— (all titles)
MCP_TRANSPORT_TYPE	Transport: stdio or http.	stdio
MCP_HTTP_PORT	Port for the HTTP server.	3010
MCP_AUTH_MODE	Auth mode: none, jwt, or oauth.	none
MCP_LOG_LEVEL	Log level (RFC 5424).	info
STORAGE_PROVIDER_TYPE	Storage backend.	in-memory
OTEL_ENABLED	Enable OpenTelemetry instrumentation.	false

See .env.example for the full list of optional overrides.

The eCFR mirror

The codified CFR is large (~50 titles, hundreds of MB of XML — Title 40 alone is ~150 MB) but changes far less often than it is queried. This server mirrors it once into an embedded SQLite + FTS5 index and serves regulations_get_cfr_section (current single sections) and regulations_browse_cfr (full-text search) from it, falling back to the live eCFR API when the mirror has not yet completed an init or a historical/whole-part read is requested.

The mirror answers only what it holds. A scoped mirror (ECFR_MIRROR_TITLES) is consulted for a search only when the requested title is in the set, and never for an all-titles search — a three-title index reporting zero matches for the whole CFR is worse than no index at all. Those requests go to live eCFR instead, and every search result names the corpus that answered it in sourceScope.

The mirror is populated out-of-band, never on startup — a full title sweep takes a while and must not block the server. Build it with:

# Mirror all 50 CFR titles (idempotent, resumable from the persisted cursor)
bun run mirror:init

# Or scope to specific titles to build a smaller, faster mirror
ECFR_MIRROR_TITLES=21,40 bun run mirror:init

# Incremental refresh against the latest eCFR issues
bun run mirror:refresh

# Report row counts, the last-synced issue date, and whether the index is stale
bun run mirror:verify

A sync pass deletes only what it read in full. Each title's pass removes the rows the pass did not rewrite — how a withdrawn section leaves the index. A response that arrives cut short parses to a prefix of the title, which is indistinguishable from a title that shrank, so the pass first checks that the document it read is whole (its root element is closed) and leaves the title untouched when it is not, rather than deleting everything past the cut and reporting the run complete.

An index written by an older ingester is not served. The ingester stamps a version into the mirror once a run has re-derived every title the index holds; when a release changes how rows are derived, an index carrying an older stamp is treated exactly like a cold one — every read falls back to live eCFR until bun run mirror:refresh re-derives it. mirror:verify says so explicitly, and a refresh removes the rows the previous ingester filed under keys the current one no longer produces. A run that skips a title — a failed fetch, or an ECFR_MIRROR_TITLES scope narrower than the index — names it in the log and leaves the stamp unwritten, because those untouched titles are exactly the ones a stamp would certify wrongly.

Until the mirror has completed an init, the codified-text tools run against the live eCFR API — so the server is useful immediately on a fresh deploy; the mirror is a latency/throughput optimization, not a hard dependency. On the HTTP transport a weekly refresh is scheduled automatically (ECFR_MIRROR_REFRESH_CRON); stdio operators run the lifecycle scripts above.

The mirror database (./data/ecfr-mirror.sqlite) is a local artifact — it is git-ignored and excluded from the .mcpb bundle, never shipped in the package.

Running the server

Local development

• Build and run:

  # One-time build
  bun run rebuild
  
  # Run the built server
  bun run start:stdio
  # or
  bun run start:http
  

• Run checks and tests:

  bun run devcheck   # Lint, format, typecheck, security, changelog sync
  bun run test       # Vitest test suite
  bun run lint:mcp   # Validate MCP definitions against the linter rules
  

Docker

docker build -t federal-regulations-mcp-server .
docker run --rm -e REGULATIONS_GOV_API_KEY=your-key -p 3010:3010 federal-regulations-mcp-server

The Dockerfile defaults to HTTP transport, stateless session mode, and logs to /var/log/federal-regulations-mcp-server. The build stage installs dependencies with --ignore-scripts — better-sqlite3 is a build/ingest-only dependency whose native compile is skipped, and the runtime reads the mirror through Bun's built-in bun:sqlite. Populate the mirror in a running container with docker exec <container> bun run mirror:init; mount a volume over /usr/src/app/data so the synced index survives container recreation. OpenTelemetry peer dependencies are installed by default — build with --build-arg OTEL_ENABLED=false to omit them.

Project structure

Directory	Purpose
src/index.ts	createApp() entry point — registers tools/resources, inits the three services, and schedules the mirror refresh on HTTP.
src/config	Server-specific environment variable parsing and validation with Zod.
src/mcp-server/tools	Tool definitions (*.tool.ts) — the seven regulations_* tools.
src/mcp-server/resources	Resource definitions (*.resource.ts) — the document and CFR-section resources.
src/services/federal-register	Federal Register API v1 client (keyless).
src/services/ecfr	eCFR API client (keyless) — versioner, structure, search, and section XML parsing.
src/services/ecfr-mirror	eCFR codified-text mirror (MirrorService — SQLite + FTS5) and its read path.
src/services/regulations-gov	Regulations.gov v4 client (X-Api-Key) — dockets and comments.
scripts/ecfr-mirror-*.ts	Out-of-band mirror lifecycle: init, refresh, verify.
tests/	Unit and integration tests mirroring src/.

Development guide

See CLAUDE.md for development guidelines and architectural rules. The short version:

• Handlers throw, framework catches — no try/catch in tool logic
• Use ctx.log for request-scoped logging, ctx.state for tenant-scoped storage
• Register new tools and resources via the barrels in src/mcp-server/*/definitions/index.ts
• Wrap external API calls: validate raw → normalize to the domain type → return the output schema; never fabricate missing upstream fields

Contributing

Issues and pull requests are welcome. Run checks and tests before submitting:

bun run devcheck
bun run test

Data disclaimer

eCFR content is "authoritative but unofficial" per the Office of the Federal Register — it is not the official legal edition of the Code of Federal Regulations. The official CFR is published annually in print and digitally at govinfo.gov. For legal research requiring the official text, verify against govinfo.gov or the annual printed CFR.

This server is not affiliated with or endorsed by the Office of the Federal Register (OFR), the Government Publishing Office (GPO), or the General Services Administration (GSA).

License

Apache-2.0 — see LICENSE for details.