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

Annotations already establish this as a read-only, idempotent, open-world call, so the safety profile is covered. The description adds genuinely new operational context with 'Paid per call from your Stratum API balance, or use a test key', which an agent needs in order to warn about cost. It stops short of explaining billing on failed lookups or what 'warning flags' actually contains.

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 sentences: the first front-loads what the tool returns, the second delivers the cost warning. No filler, no redundancy with the title.

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 single-parameter lookup with no output schema, the description is largely sufficient: it discloses the payload contents and the billing model. Minor gaps remain around failure behavior for unknown company numbers and whether officer listings are paginated or complete.

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, companyNumber, and the schema already documents it at 100% coverage with an example. The description adds nothing about the identifier format, so baseline 3 applies since the schema carries the full burden.

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?

Names a specific verb-less but concrete resource: the Companies House record for a UK company, and enumerates its contents (details, active officers, warning flags). This separates it reasonably from siblings like company_owners and company_risk_score, though the overlap with 'active officers' versus a dedicated owners tool is not addressed.

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?

No statement of when to use this versus company_owners, company_risk_score, or fca_firm, and no prerequisites such as valid registration numbers or key requirements beyond the passing 'use a test key'. The only guidance is a billing note, which is cost information rather than usage routing.

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