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

Annotations only cover the safety profile (readOnly, idempotent, openWorld, non-destructive). The description goes well beyond them by disclosing that validation is offline, the x402/Base payment model ($0.002 per call), the prepaid x-credit-token header for unlimited calls, the 1 free call/day allowance, and that no API key is required — exactly the auth/pricing behavior an agent needs.

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 definition is dense and front-loads the covered formats before the operational details. The opening 'EORI, EIN, TCKN and friends — format first' is slightly cryptic, but the pricing/auth block earns its space by answering questions an agent would otherwise have to ask.

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 an output schema present, return values need not be explained, and the description covers scheme list, the registration caveat, required inputs, and the payment/auth model. The one real omission is the set of valid 'kind' values, which matters given there are no enums.

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%, but the schema's own descriptions are placeholders ('Kind', 'Identifier'), so the baseline is 3. The description usefully clarifies that 'kind' selects the scheme, yet it never enumerates the accepted kind values (no enums present), leaving the agent to guess the exact strings.

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 names the resource precisely (offline tax/customs ID formats) and enumerates the covered schemes — EORI, US EIN/SSN, UK NINO, AU ABN, TR VKN/TCKN, CA BN — which differentiates it from generic 'check' siblings. The verb is only implied ('format first'), and it never contrasts itself with the adjacent vat_check, iban_check or bic_check 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?

'kind= selects the scheme' plus the caveat 'A well-formed id is not proof of registration' give real context on how and why to use it. However there is no explicit when-to-use vs alternatives guidance and no routing away from the sibling vat_check / iban_check tools, leaving usage largely inferred.

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