Lookup Tax ID via VIES (EU VAT Validation)

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

Annotations already declare readOnlyHint=true and destructiveHint=false. Description adds that it returns company name, address, and validity status from official EU registry, which is consistent. No contradictions; behavioral traits are well disclosed.

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 concise sentences in English followed by Spanish translation (appropriate for bilingual context). Front-loaded with purpose and key usage instruction. No superfluous content.

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 lookup tool with output schema implied, description covers purpose, usage, parameters, and expected output. Mentions intra-EU invoicing compliance context. No gaps given tool complexity.

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% with descriptions. Description adds example values and clarifies that vatNumber is without country prefix, providing additional meaning beyond schema. Lowers cognitive load for agent.

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?

Description clearly states the tool validates an EU VAT number via VIES system, with specific verb 'validate' and resource 'EU VAT number'. It distinguishes itself from siblings as the only VAT validation tool among many invoice and accounting tools.

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?

Provides clear guidance: 'always validate before adding a EU client', essential for intra-EU invoicing compliance. Includes an example. Does not explicitly mention when not to use, but context makes usage clear; no direct alternative tool exists among siblings.

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