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

Adds substantial context beyond the annotations: facts-only output with NaTHNaC prose excluded, the UK-is-NO_DATA-not-empty-list edge case, the per-row source link, the disclaimer that is prepended to every response, and the data-as-of-dates caveat. The annotations only cover safety/idempotency, so this fills a real gap.

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?

Purpose and return contents are front-loaded, and the sentences are dense but mostly load-bearing. The trailing disclaimer/caveat sentences are somewhat hedged, but they encode real behavioral requirements rather than padding.

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 structure need not be described, and the description still covers edge cases (UK NO_DATA), scope (UK travellers), and caveats. An agent has everything needed to select and call 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 description coverage is 100%, and the schema already states the ISO alpha-2 format and the precedence rule ('Ignored when `country` is given'). The description adds the side-by-side framing but little syntax or format detail beyond the schema, so the baseline 3 applies.

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+resource with unusual precision: what the tool returns (yellow-fever certificate position, country yellow-fever risk, recommended vaccine names, malaria guidance, FCDO health-risk names) and the source (TravelHealthPro/NaTHNaC). An agent can distinguish this from travel_advice or compare_healthcare without opening any 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?

Clearly routes the two invocation modes ('Give `country` for one country or `countries` (two or more) for a side-by-side') and scopes the audience ('recommendations for UK travellers... a clinic decides for a person'). It does not explicitly name a sibling alternative or state when NOT to use it, so it falls short of a 5.

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