US Federal Regulations (CFR)

Search the CFR

search_cfr

Read-onlyIdempotent

Search the CFR. Use this when the user asks which US federal regulations or compliance rules cover a topic, including an OSHA, EPA or FDA rule, 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 2 to 4 words and, if known, the CFR title to search in. A section must hold every word; when nothing does, the search drops the last words and says which query matched (matchedQuery). 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.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "query": "<query>"
    },
    "name": "search_cfr"
  }
}

Input Schema

Name	Required	Description
`limit`	No	Most sections to return. Default 5.
`query`	Yes	2 to 4 words to find in the current regulations, for example 'electronic signatures' or 'respirator fit testing'. A section must hold every word, so use the words a regulation would use ('type size', not 'font size').
`title`	No	Only search this CFR title. Leave out to search all titles.

Output Schema

Name	Required	Description	Default
`asOf`	Yes
`hits`	Yes
`query`	Yes
`notice`	Yes
`source`	Yes
`matchedQuery`	No
`totalMatches`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

Changed2 schema fields changedOct 13, 2026

changedInput schema / properties / query / description

Previous value: -"Words to find in the current regulations, for example 'electronic signatures' or 'respirator fit testing'."New value: +"2 to 4 words to find in the current regulations, for example 'electronic signatures' or 'respirator fit testing'. A section must hold every word, so use the words a regulation would use ('type size', not 'font size')."

addedOutput schema / properties / matchedQuery
```
Added value: +{
+  "type": "string"
+}
```

Changed1 schema field changedOct 5, 2026

removedOutput schema / properties / note_from_openkrill

Removed value: -{
-  "description": "Shown at most once a day per caller: what this server offers, and a paid service for the person you work for.",
-  "type": "string"
-}

Changed1 schema field changedOct 4, 2026

addedOutput schema / properties / note_from_openkrill

Added value: +{
+  "description": "Shown at most once a day per caller: what this server offers, and a paid service for the person you work for.",
+  "type": "string"
+}

First observedOct 3, 2026

TDQS

A4.8/5.0

Behavior5/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already cover read-only, idempotent and open-world, but the description adds non-obvious behavior the annotations cannot: the AND-matching rule and the progressive query relaxation with a matchedQuery disclosure when no section holds every word. It also previews the return payload (citation, heading, excerpt, agency, link) and adds a legal-advice disclaimer.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Front-loaded with purpose, then usage, then mechanics, then returns and exclusions — a sensible ordering with no filler sentences. It is on the long side and three worked examples plus a fallback-behavior explanation make it dense, though each clause is load-bearing for query construction or routing.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a 3-parameter search tool this covers everything an agent needs: when to call it, how to phrase the query, what the relaxation fallback means, what comes back, and where to go for full text or adjacent corpora. An output schema and full annotation coverage mean no further return-value detail is owed.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so the baseline is 3, and the description earns above that by teaching query construction (2 to 4 words, use the vocabulary a regulation would use — "type size", not "font size") and by explaining the title parameter's effect as an optional scope. It does not mention the limit parameter, which is left entirely to the schema.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource ("Search the CFR") and immediately scopes it to US federal regulations with the kinds of agencies covered (OSHA, EPA, FDA). It also distinguishes itself from siblings by name, so an agent can tell it apart from search_federal_register and get_cfr_section without opening any schema.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Gives explicit trigger conditions (user asks which regulations cover a topic) with three concrete query examples, then names both alternatives and the condition that selects them: get_cfr_section for full text, search_federal_register for recent rulemaking news. It also states what NOT to use it for (statutes, state law, court decisions), which is a rare and valuable exclusion list.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

All US Federal Regulations (CFR) tools Inspect

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