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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint, so the safety profile is covered. The description adds real behavioral context: what the numbers mean (percentile finalisation times), that figures carry a Home Affairs publication date, and that the single-subclass mode attaches Home Affairs notes. It stops short of stating caching/freshness or result-size 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?

Two sentences, no filler, and the payload description is front-loaded before the parameter guidance. The first sentence is dense (percentiles, subclass, stream, publication date) but every clause carries information an agent needs to interpret the result.

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 still explains the shape of the return (four percentiles per subclass/stream plus the Home Affairs publication date) and the two invocation modes. Locale-driven language/URL behavior is left entirely to the schema, which is reasonable given 100% coverage.

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, and the baseline is 3. The description adds only the behavioral distinction between supplying vs omitting visaSubclass ('with Home Affairs notes' vs 'list every subclass'); it adds nothing about the locale parameter beyond what the schema states.

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 ('Home Affairs global visa processing times') and goes further by naming the exact metric returned (25/50/75/90th percentile finalisation days, per subclass and stream, with publication date). This clearly separates it from siblings like get_visa_fees and estimate_189_invitation without needing their schemas.

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?

Explicitly tells the agent how to drive the tool: pass visaSubclass for a single visa (returned with Home Affairs notes) or omit it to enumerate every subclass. That is clear usage context, though it does not name an alternative sibling tool or state exclusions (e.g. when another tool is better).

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