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

Annotations already declare readOnlyHint, openWorldHint, and destructiveHint=false, so safety is covered. The description adds non-obvious behavior beyond that: a 5-credit cost, the paid-plan gate on bulk destination listing, and that it returns allowed stay in days where one is set.

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?

Front-loaded with what the tool returns, followed by two short supporting sentences about output detail, plan gating, and cost. Minor redundancy in restating 'Visa Requirements: Visa Requirements tells you...' which duplicates the name and title.

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?

For a two-parameter lookup with a full output schema and annotations, the description covers outcome types, optional-destination behavior, plan limits, and cost. Remaining gaps (invalid-code handling, territory vs country semantics) are modest and partly absorbed by the schema's examples.

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%, so both parameters are already documented with formats and examples, meeting the baseline. The description adds only the implication that destination can be omitted for a full listing, without explaining formats or matching behavior itself.

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 and resource ('tells you what a passport holder needs to enter another country') and enumerates the exact outcome categories returned (no visa, ETA, eVisa, visa on arrival, visa in advance, restricted). This makes it clearly distinguishable from the many country-data siblings such as CountryLookup, CountryBorders, or CountryLanguages.

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?

Explains the operating modes: passport is required, and omitting destination lists every destination for one passport, but only on paid plans. That is clear contextual guidance for how to invoke the tool, though it names no alternatives or exclusions (e.g., what to do for multi-passport comparisons).

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