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

Annotations already declare readOnly, idempotent, non-destructive and open-world, so the safety profile is covered; the description adds genuinely new behavioral context on top: 'where available' signals incomplete coverage, the fields 'are not independently verified by CelerAPI' discloses data provenance/trust limits, and the x402 price on Base mainnet tells the agent a paid call is involved. It stops short of explaining any rate limits, pagination, or empty-result behavior beyond the availability caveat.

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?

Three sentences organized as purpose, field content, use cases, with the core verb and scope front-loaded and no filler. The pricing sentence is useful but sits somewhat detached at the end rather than being integrated into the operational guidance.

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?

An output schema exists, so return values need no explanation, and annotations cover the safety profile; the description fills the remaining gaps an agent would care about: data trust, field availability, cost. It leaves minor operational details (empty-result handling, whether resigned officers are included by default given the 'resignation details where available' phrasing) unstated.

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% and the single company_number parameter is fully documented in the schema (format pattern, source sibling search_company, example). The description only implies that the identifier is a UK Companies House number and adds no syntax or sourcing detail beyond what the schema already provides, so baseline 3 applies.

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 and resource ('Retrieve directors and other officers recorded for a UK company at Companies House'), which is far more precise than the tool name alone. The 'UK company / Companies House' scoping implicitly distinguishes it from the parallel get_entity_officers sibling, but that sibling is never named, so the differentiation is inferential rather than explicit.

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?

Enumerates concrete use contexts (due diligence, governance research, supplier onboarding, public-register verification), which gives an agent a clear sense of when the tool is appropriate. There are no exclusions or named alternatives ('use X instead when...'), so it falls short of the top band.

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