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

With no annotations provided, the description fully discloses behavioral traits: cost ($0.02 USDC per call), the exact return structure (`result.fca` with fields `checked, regulated, frn, firm_name, status, permissions_summary, warnings[], note`), error handling ('never a 500', register unavailable leads to `checked=false` with a reason), and that it is a separate call from the verdict. No contractions exist.

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?

The description is concise and well-structured: it opens with the core question, then lists returns, cost, and error behavior. Every sentence adds value without extraneous text. It is front-loaded with purpose and efficiently organized.

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 tool with one parameter, no output schema, and no annotations, the description is fully complete. It covers purpose, return shape, error case, cost, and differentiation from sibling. The agent has all necessary information to invoke the tool correctly.

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?

Schema coverage is 100% for the only parameter (`number`), with a clear pattern and description. The description does not add additional semantics about the parameter beyond what the schema provides, so the baseline score of 3 is appropriate. No repetition or contradiction.

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 clearly states the tool's purpose: checking if a UK company is FCA-regulated and returning register status, permissions summary, and warnings. It uses a specific verb ('returns') and identifies the resource (FCA register), and explicitly distinguishes from the sibling tool `uk_company_verdict` by noting it is 'sold separately from the full verdict'.

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 provides clear context by noting 'fintech-vetting agents often want only this', implying the tool is for quick FCA checks without the full verdict. It hints at the alternative (the verdict tool) by mentioning 'sold separately', but does not explicitly state when not to use this tool or name the alternative directly. Still, the guidance is effective.

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