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

With no annotations, the description carries the full burden. It does disclose the authoritative source (official European Commission EOS API) and the shape of the result ('valid/invalid and name/address when disclosed'), which is genuinely useful given there is no output schema. It omits failure behavior for malformed input, rate limits, and any auth requirements.

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 short sentences with no filler; the core action is front-loaded and the supporting detail (API source, return content) follows. Every sentence earns its place.

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?

Since no output schema exists, the description correctly takes on the job of describing return values ('valid/invalid and name/address when disclosed'). For a one-parameter lookup this is nearly complete, with only input-validation and error behavior left undocumented.

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 0%, so the description must compensate. It supplies a concrete example ('SE5560360793') that communicates the expected format (country prefix plus digits), which is real added value, but it gives no constraints on length, allowed country codes, or handling of lowercase/whitespace.

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 and resource ('Verify one EU EORI ... number'), names the domain (EU EORI), and the word 'one' implicitly separates it from the sibling verify_eori_batch. An agent can route between singular and batch verification without opening either schema.

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?

Usage is implied rather than stated: verifying a single EORI. There is no explicit when-to-use vs. when-not guidance, no mention of when to prefer verify_vat or verify_eori_batch, and no stated prerequisites (e.g., the input must already be an EORI, not a VAT number).

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