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

Annotations already declare readOnlyHint, openWorldHint, idempotentHint, and destructiveHint=false, so the safety profile is covered. The description adds meaningful behavior beyond annotations: it states the checks are live against VIES, describes the per-row result structure, and discloses pricing per check.

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 question it answers and avoids unnecessary repetition. The audience sentence and pricing note are useful, though the middle sentence is long and could be tightened.

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 five-parameter, all-optional validation tool with no output schema, the description gives enough context: it explains the live data source, what each row contains, and the two validation standards. It does not cover edge cases such as partial failures or empty arrays, but the core invocation context is complete.

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 all five parameters are already documented. The description adds some meaning by explaining that expectedName is matched against the company behind the VAT numbers, but overall it does not add much beyond the schema's own parameter descriptions.

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 specific verbs and resources: checking EU VAT numbers live against VIES and validating IBANs against ISO 13616. It clearly explains what is validated and what is returned per row, though it does not explicitly distinguish itself from sibling tools such as company_check or identifier_resolver.

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 names intended use cases like supplier onboarding, invoice checks, and KYB, which implies when to use the tool. However, it gives no explicit when-not guidance and does not compare itself with sibling tools that might also be relevant.

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