Rules Lookup in Claude
US federal regulations (CFR). The MCP server is https://rules.openkrill.app/mcp. No key. The steps below are only for Claude. A call to get_cfr_section was checked against that server on 2026-10-01.
What this server answers
Read the rule itself instead of a summary of it. Ask "what does 21 CFR 11.10 say?", "which regulations mention respirator fit testing?" or "what has the FDA proposed on food dyes this year?".
Rules Lookup reads two official United States sources directly: the Electronic Code of Federal Regulations (eCFR) for the current text of any section of the Code of Federal Regulations, and the Federal Register for the rules, proposed rules, notices and presidential documents the agencies publish each day.
A section lookup returns the citation, heading, full text, statutory authority and amendment history of the section, with the date the eCFR is up to date as of and a link to the section. A very long section is cut and says so. A search returns the matching sections or documents with the agency, the publication date, the comment deadline and effective date where there is one, and the CFR parts a document changes.
This is general information, not legal advice. The eCFR is an unofficial edition kept up to date by the Office of the Federal Register; the legal text is the Federal Register and the annual CFR. A rule applies differently to each situation, so check the current official text and ask a qualified lawyer before you rely on it.
It covers United States federal regulations only: not state or local law, court decisions, statutes, other countries' rules or guidance documents that are not in the Federal Register.
It stores nothing about you: answers are cached for up to six hours (sections) or an hour (searches), and the only lasting record is a daily count of calls per tool.
What it can do
- Reads the current text of any section of the US Code of Federal Regulations (eCFR)
- Shows a section's heading, statutory authority and amendment history with a link
- Searches the current regulations by words, in one title or all of them
- Searches the Federal Register for rules, proposed rules, notices and executive orders
- Shows comment deadlines, effective dates and the CFR parts a document changes
Tools
get_cfr_section, Read a CFR section. Use this when the user asks what a specific US federal regulation says or cites one, for example "what does 21 CFR 11.10 say?", "read 29 CFR 1910.134" or "show me 17 CFR 240.10b-5". Pass the CFR title number and the section number. Returns the current text, heading, statutory authority and amendment history of the section, the date the eCFR is up to date as of and a link to it. A very long section is cut and flagged. This is general information, not legal advice. Do not use it to find a regulation by topic (use search_cfr), for statutes, state law or court decisions, or to decide whether someone complies.search_cfr, Search the CFR. Use this when the user asks which US federal regulations cover a topic, for example "which regulations mention respirator fit testing?", "find the rules on electronic signatures in title 21" or "where does the CFR define small business?". Pass the words to find and, if known, the CFR title to search in. Returns the best matching sections with citation, heading, an excerpt, the agency and a link; use get_cfr_section to read one in full. This is general information, not legal advice. Do not use it for recent rulemaking news (use search_federal_register), statutes, state law or court decisions.search_federal_register, Search the Federal Register. Use this when the user asks what federal agencies have published, proposed or announced, for example "what has the FDA proposed on food dyes?", "find final rules on noncompete agreements" or "which executive orders mention AI this year?". Pass the words to find and optionally the document type (rule, proposed_rule, notice, presidential_document) and a publication date range. Returns each document's title, type, agencies, publication date, abstract, effective date, comment deadline, the CFR parts it changes and a link. This is general information, not legal advice. Do not use it to read the current text of a regulation (use get_cfr_section), or for state law, bills, court decisions or non-US rules.
Add Rules Lookup in Claude
Claude connects to a remote MCP server as a custom connector. The connection is made from Anthropic's cloud, not from your laptop, so the server must be on the public internet. Rules Lookup is. These steps were checked against Claude's custom-connector article (updated 2026-08-11) and the Claude Code MCP docs on 2026-10-01.
On a Pro or Max plan:
- Open Customize, then Connectors.
- Select the plus button, then Add custom connector.
- Paste
https://rules.openkrill.app/mcp. Leave Advanced settings empty: this server does not need an OAuth client id or secret. - Select Add. The connector is yours. Anthropic has not reviewed it, and it is not a Directory listing.
- In a conversation, open the plus button, then Connectors, and enable Rules Lookup. Ask: What does 21 CFR 11.10 say about electronic records controls?
On Team and Enterprise, an Owner adds the connector first at Organization settings, then Connectors, then Add, then Custom, then Web, and pastes the same URL. Members then connect it from Customize. A Free plan can add one custom connector.
In Claude Code, add it from the project directory:
claude mcp add --transport http rules https://rules.openkrill.app/mcpThat writes a local or user config. A JSON entry needs "type": "http" (or streamable-http) plus the url. An entry with a url and no type is skipped. Confirm with claude mcp get rules. The tools you should see are get_cfr_section, search_cfr, search_federal_register.
Enable the connector only in conversations that need it. Claude can call the tools while you work, including during research, so turn off any tool you do not want invoked. Rules Lookup does not write to your accounts. It still receives the arguments of each call. Read the privacy page before you paste anything that is not public.
A call checked on 2026-10-01
21 CFR 11.10 is the electronic-records section named in the plugin's starter prompts. The request below was posted to https://rules.openkrill.app/mcp as tools/call. HTTP 200. Source: the Rules Lookup server, read 2026-10-01.
{
"method": "tools/call",
"params": {
"name": "get_cfr_section",
"arguments": {
"title": 21,
"section": "11.10"
}
}
}- asOf. 2026-09-29
- source. Electronic Code of Federal Regulations (eCFR, ecfr.gov), Office of the Federal Register
- heading. Controls for closed systems.
- citation. 21 CFR 11.10
- notice. The eCFR is an unofficial, continuously updated edition of the Code of Federal Regulations. The legal text is the Federal Register and the annual CFR on govinfo.gov. This is general information, not legal advice. Regulat
- url. https://www.ecfr.gov/current/title-21/section-11.10
Repeat the call yourself if you need a newer reading. Cached answers expire. A rate limit is not a result: wait and try again. Nothing in the call is a ranking, a filing, or advice.