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

Beyond the annotations (readOnlyHint, openWorldHint, destructiveHint), the description discloses critical behavior under provider outage or unknown status, stating it returns 'unavailable'/'needs_review' and never a false 'invalid'. It also clarifies the configuration dependency and disclaims legal/customs decision authority, adding substantial transparency.

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 description is three sentences, front-loaded with the core purpose, and every sentence contributes unique value (function, edge-case behavior, limitations). No redundant or filler content exists.

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 single-parameter input, existing output schema, and annotations, the description covers the key operational aspects: conditional behavior, provider unavailability, the meaning of structural validity, and disclaimers. It is sufficiently complete for an agent to understand when and how to use it.

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?

The input schema fully describes the 'eori' parameter with an example and length constraints (100% coverage). The description does not add further parameter-level semantics beyond the schema, so the baseline of 3 is appropriate.

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 explicitly states the tool performs a 'structural check' and, conditionally, an 'authoritative existence check' of an EORI number. This clearly differentiates it from siblings that handle import measures, costs, receipts, and tariff codes.

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 context that this is a read-only preflight used for EORI validation, and it cautions against relying on structural validity as proof of customs authorisation. However, it does not explicitly name alternative tools for exclusion, so it falls short of a full 5.

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