companies_house_company

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

With no annotations, the description carries the full burden; it does disclose the COMPANIES_HOUSE_API_KEY auth requirement, which is real added value. However, it says nothing about error behavior for an unknown number, rate limits, or what the record contains, so a 3 is appropriate.

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?

One front-loaded sentence, no filler, the key constraint ('one', 'by number') precedes the parenthetical auth note.

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 covers purpose and the auth requirement adequately. Minor gaps remain around expected return shape and invalid-number handling, but nothing critical for invocation.

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 0% on a single required parameter, so the schema alone says nothing. The phrase 'by number' clarifies that the parameter is the company number identifier, which is partial compensation, but no format guidance (e.g., 8-character CRN) is given.

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 (Fetch), resource (UK company record), and a scope qualifier (one, by number) that implicitly separates it from the sibling companies_house_search. It does not explicitly name the search sibling, so it stops 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?

'by number' implies you must already hold a company number, which is useful, but the description never states when to use this over companies_house_search (e.g., when you know the number vs. when you need to look one up). Usage is inferable but not spelled out.

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