get_contacts

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

With no annotations, the description carries the full behavioral burden. It usefully discloses the separate metering/billing trait and the validation state of the data, but says nothing about permissions, failure behavior for non-UK companies, or rate limits beyond cost.

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 the returned content and then the cost warning. The em-dash clause is slightly loose but every clause carries information; nothing is wasted.

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?

No output schema and no annotations, so the description is the only source of shape information. It lists what comes back but not the structure of the returned payload (single vs list of emails/phones), which is a notable gap for a tool whose output is the whole point.

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% for the single required parameter, so the description must compensate. It adds the useful framing that the identifier is a UK company number, but does not state the format (e.g. Companies House 8-character number), leaving the schema to carry the rest.

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 names a specific resource (contact details for a UK company) and enumerates the returned fields — SMTP-validated emails, phone, website domain. That distinguishes it from search_companies and get_company, though it does not name a sibling explicitly.

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 gives a clear usage condition: metered separately, use sparingly, only when the user actually needs contact details. That is a real when-to-use rule, but it never names the cheaper alternative (get_company) that an agent should prefer for general company data.

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