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

With zero annotations, the description carries the full burden. It discloses the output shape (up to 10 candidates with name, legal_name, city, domain), the error response format, and the purpose of the return (slug consumption). It does not mention permissions, rate limits, or side effects, but this is a lookup tool and those details are not critical.

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 uses three sentences that all earn their place: purpose, output, error condition, sibling pointer. It is denser than necessary but not padded, and avoids repeating parameter descriptions already in the schema.

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?

No output schema exists, so the description must cover the return contract and it does. It covers error cases, candidate fields, the relationship to get_agency_profile, and reminds of the alternative. Missing bits are minor (e.g., default limit/value range is schema-covered, not description-critical).

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% and the description adds meaning beyond the schema: it clarifies the name/domain mutual requirement (neither given -> error), that 'name' accepts either trade or statutory name, and the domain format. Even with a baseline of 3, the additional context nudges it to 4.

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?

States a specific verb (find/look up) and a specific resource (one agency) with concrete identifiers (trade name, statutory name, domain). It explicitly contrasts with search_agencies (ranked recommendations) and get_agency_profile (consumer of the slug), so an agent can instantly tell it apart.

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?

Directs when to use: when you need a specific agency's slug, and when not to (search_agencies for ranked recommendations). It also states the requirement that name or domain must be provided, and the condition that triggers an invalid_input error.

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