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

No annotations are provided, so the description carries the full burden and does well: it discloses batching (up to 10), the free format pre-check that filters typos before a billed call, the live-vs-cached nature, the cost model (paid per call via x402 USDC on Base), and the conditional return of name/address only where trader consent exists.

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?

Dense but front-loaded: identity and scope first, then return shape, then the format pre-check benefit, then usage trigger, then cost. Every sentence contributes operational information with no filler.

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 and no annotations, the description compensates by describing return fields (valid/invalid per number, request date, consented name/address), batching limits, and cost. Nothing an agent needs to invoke this correctly is missing.

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 schema fully documents both parameters, including the comma-separated batch syntax and the PAYMENT-SIGNATURE header. The description only echoes the batch limit and alludes to the paid model, adding little beyond what the schema already states. Baseline 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?

States a specific verb (validate) and resource (EU EORI numbers), scoped to all 27 EU states plus XI Northern Ireland, and names the authoritative source (European Commission's official service). An agent immediately knows what the tool does and against what data.

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 a concrete when-to-use trigger: shipping, invoicing, or clearing customs with an EU trader and needing confirmation of validity in the official register. No alternatives exist (no siblings), so it cannot differentiate, but the usage context is explicit.

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