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

Annotations already declare readOnlyHint, destructiveHint=false and openWorldHint=false, so the closing 'Read only.' merely repeats structured data and earns no credit. The one piece of added behavioral context is provenance ('source (official government pages where available)'), which tells the agent how much to trust the answer; nothing is said about coverage gaps, missing pairs, or failure behavior.

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?

A single front-loaded sentence whose colon list previews the response fields before any caveats. Every clause carries information; the only near-redundant element is the trailing 'Read only.'

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 takes on the job of describing return values (rule name, processing days, source) and the official-sources caveat. What is missing is the edge case: what the tool returns when no rule exists or when a passport/destination pair is unsupported.

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 100%, so the baseline is 3, and the description adds real meaning by stating the query is evaluated 'for each passport and each destination country' — i.e. the two arrays are combined pairwise rather than interpreted as one aggregate request. The 6-item maxItems bounds are left to the schema, which 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 names the specific decision being answered ('whether travellers need a visa or an electronic authorisation') and enumerates what comes back ('the rule's name, the minimum processing days and its source'), which is far more than a restatement of the tool name. It does not explicitly contrast with any sibling, though no sibling in the list covers entry rules, so the differentiation is implicit in the subject matter.

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?

Usage is implied by the phrasing 'for a holiday' and by the per-passport/per-destination framing, which tells an agent this is a trip-planning lookup. There is no explicit when-to-use, no prerequisites, and no mention of an alternative when the answer is unknown or the country pair is out of scope.

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