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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds value beyond them by disclosing the response shape (entry type plus permitted stay in days 'when known') and a real coverage limitation: short tourist stays only, not work/study/residence. It stops short of noting data freshness or how gaps in coverage are signalled, so it is not a full 5.

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?

Three tight sentences, front-loaded with the triggering question, then the return values, then the scope exclusion. No filler, and every sentence carries distinct information.

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 no output schema, the description correctly compensates by naming the returned entry-type categories and the stay-in-days field, and it bounds the domain to tourist stays. What is missing is any relationship to the sibling calculate_schengen_days for multi-country itineraries, which an agent handling travel questions would likely need.

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%: both parameters are documented in the schema with the ISO 3166-1 alpha-2 format and examples. The description adds no syntax, case, or format detail beyond that, so the baseline of 3 for high-coverage schemas 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 gives a specific verb+resource ('check visa requirement') and immediately narrows scope: it answers whether a visa is needed and how long one may stay for a given passport. It also enumerates the exact return categories (visa free, visa on arrival, e-visa, visa required), which lets an agent distinguish it from siblings like calculate_schengen_days 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?

It states a clear trigger ('when someone asks whether they need a visa to visit a country, or how long they can stay') and an explicit exclusion ('Do not use it for work, study or residence permits; it covers short tourist stays only'). The one gap is that it never names an alternative tool for the excluded cases or for Schengen day-counting, which is what a 5 would require.

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