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

Annotations already declare readOnly, idempotent, openWorld, non-destructive, so the safety profile is covered. The description adds real value beyond that: the upstream data source (EC EOS), the 10-item batch cap, and the fact that name/address are only returned where the operator consented to publication — a meaningful data-availability caveat.

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 compact sentences, front-loaded with the core question, then the source and the batch/return caveats. Nothing is redundant or padded.

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, the description usefully discloses what comes back (name and address, conditionally). It is nearly complete for a simple read-only lookup, though it could say what an invalid number returns and confirm the single-vs-batch input rule.

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 50%; the eoris array description already says 'or up to 10 numbers at once', and the description merely echoes the limit. It doesn't clarify the anyOf requirement (exactly one of eori/eoris) or the EORI format (country prefix + number, max 20 chars), leaving gaps the schema alone doesn't fill.

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?

Opening question states a specific verb (validate) and resource (EORI number for EU customs), and names the authoritative source (European Commission EOS). It doesn't explicitly differentiate from the closely related vat_check sibling, so it stops short of a 5.

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 validity question implies when to use it, and 'up to 10 numbers per call' hints at batch use, but there is no explicit when/when-not guidance or mention of vat_check as the alternative for tax-ID validation.

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