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

Annotations already cover read-only, idempotent, open-world, and non-destructive behavior. The description adds substantial value beyond that: it explains the three possible status values, clarifies that `unavailable` does not mean invalid, describes when name and address are disclosed (legal-form marks) and when `personal_data_omitted` is true, notes that some countries never disclose them, and includes a legal disclaimer.

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?

The description is front-loaded with the core purpose, then efficiently layers in critical output semantics and caveats without wasted words. Every sentence contributes necessary context for interpreting the tool's results.

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?

Given the existence of an output schema and rich annotations, the description need not explain return formatting. It nevertheless completes the picture by explaining status semantics, data omission rules, country-specific disclosure behavior, and a legal caveat, leaving no major behavioral ambiguity for an agent.

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%, and both parameters have detailed schema descriptions covering format, prefix handling, and country code specifics. The description does not add any parameter-level meaning beyond what the schema already provides, so the baseline of 3 applies.

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 specific verb and resource: checks an EU VAT number in the European Commission's VIES. It is clear what the tool does, but it does not explicitly distinguish itself from sibling tools like check_eu_counterparty, peppol_lookup, or vies_country_status.

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?

The description gives no explicit when-to-use guidance, no prerequisites, and no comparison to alternative tools. It only implies usage through its stated purpose, leaving an agent to infer when this tool is appropriate versus its siblings.

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