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

No annotations exist, so the description carries the full burden. It does disclose the meaningful behavioral trait of cost ('1 credit') and implies a read-only lookup by asking for a company number, but it says nothing about empty results, invalid-number errors, or whether the data is cached or live.

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 tight sentence with the resource front-loaded and the cost tucked in parentheses. Nothing is wasted and nothing important is buried.

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 one-parameter lookup with no output schema, the definition is workable but thin: it never indicates what a PSC record contains (names, addresses, nature of control) or how to interpret an empty response. An agent can invoke it, but cannot predict its payload.

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 coverage is 100% for the single required parameter, so the baseline is 3. The phrase 'for a company number' maps the input to Companies House-style company numbers, but adds no format, prefix, or validation detail beyond that.

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 the resource precisely and expands the acronym ('Persons with significant control (beneficial owners)'), which makes the tool's data unambiguous. It lacks an explicit verb and doesn't name the sibling it differs from (e.g., company_officers), so it falls short of 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?

There is no when-to-use or when-not-to-use guidance and no mention of siblings such as company_officers, company_profile, or company_filings that an agent must choose between. The only routing signal is implicit in the resource name.

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