check_vies

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

With no annotations, the description carries the burden and does it well: it discloses that validation goes through VIES (an external EC service), that it checks current registration, and that company data is returned only when the member state provides it – a non-obvious behavior. It does not cover error handling or response format, but for a read-only check it is sufficiently transparent.

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 one concise sentence, front-loaded with the action, and includes the important caveat about member state data provision without any filler or redundancy.

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 simple tool with two parameters and no output schema, the description explains the purpose, external dependency, and variable return data. It does not specify the exact response structure for unregistered numbers, but the context provided is sufficient for basic operational understanding.

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?

Both parameters are fully described in the input schema (vatNumber without prefix, countryCode as two-letter EU code). The tool description adds no extra parameter semantics, but schema coverage is 100%, 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 uses the specific verb 'validate' with the resource 'EU VAT number via VIES', explains it confirms current registration, and mentions the return of company name/address when available. This clearly distinguishes it from sibling tools like validate_polish_id and check_vat_whitelist.

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 implies usage for EU VAT validation via VIES but does not explicitly discuss when to avoid it or mention alternative tools. Sibling tool names suggest alternatives, but the description itself lacks direct 'use this instead of X' guidance.

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