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

With no annotations provided, the description carries full burden and excels: it discloses live upstream service (EOS/DDS2), output format (valid true/false plus name/address conditionally), transport details (SOAP upstream, clean JSON out), caching behavior (24h cache), and cost ($0.003 USDC per call). This is rich behavioral context beyond what a schema or annotations would provide.

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?

Every sentence adds value: purpose, use case, parameter format, return behavior, operational details (JSON/cache), and pricing. The description is front-loaded with the primary function and is efficiently structured, with no filler or redundancy.

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?

Given the simplicity (1 param, no output schema, no annotations), the description is remarkably complete. It covers input format, expected output, conditional data availability, and cost/caching nuances. Nothing essential is missing for an agent to invoke it correctly.

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 does so fully: 'Query: ?eori=FR38347481400100 (2-letter country + up to 15 alphanumerics)' specifies the exact format and provides an example, adding essential meaning beyond the bare schema property 'eori'.

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 clearly states the tool's purpose: 'Live EORI (Economic Operators Registration and Identification) validation via the European Commission EOS/DDS2 service.' It specifies the exact resource (EORI numbers) and the action (validation), and distinguishes it from sibling validation tools (email, IBAN, SIRET, VAT, etc.) by focusing on this unique EU customs identifier.

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 description provides clear usage context: 'the number every business needs to clear customs in the EU' implies when to use it (validating an EORI for customs-related checks). It does not explicitly compare to alternatives or state exclusions, but the context makes the intended use case obvious. This matches 'clear context, no exclusions'.

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