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

Annotations establish readOnly/no-destruction, so the safety profile is largely covered. The description adds genuinely useful behavior: it is free of charge, it caps results at three matching companies with named fields, it validates VAT format and check digit, it checks domain resolution and mail servers, and it returns the price. Missing pieces are whether it consumes quota or rate-limits.

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 dense sentences, with the core purpose front-loaded before the enumeration of what is checked. The list of checks is long but each clause earns its place by telling the agent what a preview will surface.

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?

There is no output schema, so the description carries the burden of describing returns and it does so concretely (company fields, VAT validity, domain resolution, price). Combined with the annotations covering the safety profile and the schema documenting inputs, an agent has enough to call it correctly.

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%, so both parameters are already documented, which sets the baseline at 3. The description's route-specific detail (company, VAT, domain behavior) adds flavor about what each route previews, but it does not clarify the nested 'input' body beyond what the schema says.

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 states a concrete verb+resource: a free dry-run of a request against a route, returning whether it can be answered and what it would return. It implicitly distinguishes itself from the paid sibling routes (company, vat, domain) by framing itself as the pre-payment check, though it never names 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 an explicit trigger: 'Use when: you are not sure the paid call will find the right subject.' That tells the agent when to reach for preview instead of a paid route. It stops short of naming the alternative tools or stating when preview is unnecessary (e.g. when the subject is already known).

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