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

With no annotations present, the description carries the full burden and does disclose non-obvious traits: results are cached up to 24 hours, provenance is attached, and officers are capped at the first page (~35) with explicit total/coverage metadata so truncation is detectable. It does not state authentication requirements, rate limits, or behavior when a company number is not found.

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?

A single dense sentence that front-loads the resource and then the returned fields, with no filler. Every clause (officer cap, coverage metadata, cache TTL, provenance) contributes information an agent needs.

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?

There is no output schema, so the description must describe returns, and it does so thoroughly, including pagination and freshness. For a one-parameter tool this is close to sufficient; only failure modes and auth expectations are absent.

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?

Only one parameter exists and the schema documents it at 100% coverage ('Companies House number'), so the baseline is 3. The description confirms the parameter is a company number but adds no format guidance (numeric vs prefixed, e.g. SC/OC prefixes) 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 names a specific resource and enumerates exactly what it returns: status, SIC codes, registered office, accounts/confirmation dates, and first-page officers. That field list implicitly separates it from uk_company_search (search) and uk_psc_ubo (ownership), but no sibling is named explicitly, so it falls just short of full differentiation.

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?

'Primary source' implies this is the default canonical lookup rather than a cross-registry fallback, which is a useful hint. However, there is no explicit when-to-use/when-not guidance, and no routing to complementary siblings like charge_register, uk_psc_ubo, or uk_insolvency_notices for data this tool does not cover.

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