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

With no annotations, the description carries the full behavioral burden. It implies a read-only lookup and discloses the API-key requirement plus the data shape, but omits rate limits, pagination behavior beyond maxResults, and error conditions (e.g., invalid key). Adequate but with clear gaps for an unannotated tool.

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 compact sentences with no waste, and the core purpose and returned fields are front-loaded before the API-key note. Efficient, though the field enumeration slightly crowds the leading sentence.

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 5-parameter search tool with no output schema and no annotations, the description covers purpose, key prerequisite, and the shape of returned data. It would be stronger with sibling routing or rate-limit context, but nothing essential to invoking it correctly is missing.

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 description coverage is 100%, so the schema already documents every parameter including the query/companyNumbers choice and includeOfficers. The description only restates the officer roster option, adding no syntax or format detail beyond the schema, which is the correct baseline when the schema does the heavy lifting.

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 (search/look up) and resource (UK companies on the official Companies House register), and enumerates the data fields returned. It is distinguishable from siblings in spirit, but it never explicitly names alternatives like lookup_lei or resolve_company_identity, so differentiation is implicit rather than stated.

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 supplies a concrete prerequisite ("Needs your own free Companies House API key"), which is genuine usage context. However, it gives no when-to-use vs when-not guidance and does not point to any of the many sibling lookup tools, so an agent must infer the appropriate case.

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