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

Annotations already declare readOnlyHint and openWorldHint, so the description adds useful context beyond them: the x402 payment cost of $0.05 USDC per successful call when no API key is present, and the name-matching behavior of returning a best match plus other matches. It does not disclose rate limits, failure modes, or whether results are cached, but the payment and matching semantics are meaningful additions.

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 is front-loaded with the resource and query modes, then lists returned fields and pricing. The field list is long but earns its place because there is no output schema and the agent needs to know what data is available. It avoids filler and unnecessary repetition.

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?

Given a single-parameter lookup with no output schema, the description covers the key aspects: input modes, returned data fields, name-matching behavior, and payment requirements without an API key. It omits error behavior, rate limits, and explicit sibling differentiation, which keeps it from being fully complete, but the core information an agent needs is present.

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 schema already documents the single query parameter with examples for company number formats. The description restates that the query can be a company number or name, and adds that name queries return a best match plus other matches, but it provides no additional syntax or normalization details. The baseline of 3 is appropriate 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?

The description clearly identifies the resource (a UK company on the Companies House register) and the lookup input modes (company number or name). It also enumerates the returned data fields, which is valuable because there is no output schema. It does not explicitly distinguish itself from sibling tools like uk_officer_search or us_company_lookup, so it falls short of a 5.

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?

It states the two query modes and notes that a name query returns the best match plus other matches, which is useful usage context. However, it gives no explicit guidance on when to use this tool versus uk_officer_search or us_company_lookup, and there are no exclusions or prerequisites beyond the pricing note.

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