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

Annotations only declare readOnly/idempotent/openWorld, but the description discloses the data sources consulted (national registers, VIES/HMRC, sanctions lists, TLS, phishing list), the result vocabulary, and a rate-limit/quota model with a paid unlock. That is substantial behavior beyond the structured fields.

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?

Long but dense and front-loaded: the core question comes first, the signal list second, the return vocabulary and quota mechanics last. Every sentence carries information, though the enumeration of registers is slightly heavier than needed.

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?

With no output schema, the description steps in to describe the return shape (match = verified | partial | not_found | attention with per-signal evidence and field sources) and the quota/buy_url flow. An agent has everything needed to call it and interpret the result.

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%, so the baseline is 3, but the description adds genuine meaning: it explains why vat_number matters (catching a number belonging to a different or ceased company) and that country disambiguates a bare number. company_name is not elaborated, keeping it short of a 5.

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 and resource with explicit scope: 'Check a web shop BEFORE paying it' and then spells out exactly what is checked (registration, VAT, sanctions, domain age, TLS, phishing list). There are no siblings to distinguish from, but the purpose is unambiguous and self-contained.

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?

Gives explicit timing ('BEFORE paying'), the condition for the optional vat_number parameter ('from the checkout or invoice when you have it'), and an operational instruction for quota exhaustion ('show buy_url to your user'). The when-to-use and how-to-react guidance is unusually complete.

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