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

Annotations already declare readOnlyHint=true and destructiveHint=false, covering safety. The description adds meaningful behavioral detail by enumerating exactly what the tool returns, including the verbatim Federal Register API quote, which goes beyond the annotations. No contradiction exists between the description and annotations.

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

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

Two sentences with zero filler. The first sentence front-loads the purpose and full return contents; the second clarifies the identifier format and its cross-tool relevance. Every clause earns its place.

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

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

For a single-parameter, read-only tool with an output schema and safety annotations, the description is nearly complete: it covers input format, return fields, and source. The only minor gap is not stating behavior for a non-existent or malformed document number, but this is not critical given the simple operation and existing schema.

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

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

The schema already describes document_number with an example, so baseline is 3. The description adds value by explaining the format ('look like "2026-13685"') and how the parameter is obtained ('appear in every other tool's results'), which helps agents understand the parameter's provenance and expected format beyond the schema.

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

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

The description states a specific verb and resource: 'Get one rule by Federal Register document number.' It enumerates the exact fields returned (title, agency, effective date, DATES paragraph, CFR parts, publication date, link, verbatim quote), leaving no doubt about scope. This clearly distinguishes it from sibling list tools, which return multiple rules, and verify_quote, which has a different purpose.

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

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

The description notes that 'Document numbers ... appear in every other tool's results,' which clearly implies the intended workflow: obtain a document number from another tool, then call get_rule for the full record. It provides clear context but does not explicitly name alternatives or state when-not-to-use it, so it falls just short of a 5.

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