validate_company_number

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

No annotations provided, so description carries full burden. Discloses that it only checks format, specifies valid patterns (8 digits or prefix+6 digits), notes there is no check digit, and explains what prefixes denote. Clearly states what it does not do (confirm existence).

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, front-loaded with a strong imperative. Every sentence adds essential information with no waste.

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 validation tool with one parameter, no output schema, and clear sibling differentiation, the description covers purpose, usage guidelines, format details, and limitations completely.

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% (parameter 'number' has description), so baseline is 3. Description adds extra meaning by detailing valid formats and prefixes, going beyond the schema's simple description.

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 uses a specific verb ('check'), identifies the resource ('UK company number'), and clearly states it validates format and identifies register/type. It distinguishes itself from lookup_company, which confirms existence.

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?

Explicitly states when to use ('before relying on it') and what not to use it for ('does NOT confirm the company exists'). References the sibling tool lookup_company as the alternative for existence checking.

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