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

Annotations already declare readOnlyHint, idempotentHint, non-destructive and non-open-world, so the safety profile is covered. The description adds domain framing — the 90/180 rule itself and the applicability limits — which helps an agent predict the computation, though it says nothing about return format or error 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?

Three tight sentences: purpose first, input requirement second, exclusions last. No filler and no repetition of schema detail beyond what reinforces correct use.

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 read-only calculator with full schema coverage and no output schema, the description covers purpose, applicability, and input expectations. It implies the return values ('how many days used or left') but does not describe the response structure, which is the only minor gap.

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 the baseline is 3. The description goes slightly beyond it by stressing 'Pass every stay' and that past and planned stays can be mixed, which signals that incomplete input produces a wrong count — a meaningful semantic emphasis.

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 — computing Schengen days used/remaining under the 90/180 rule, plus an overstay check for planned trips. The scope is precise enough that an agent can tell it apart from a generic visa-requirement check without opening the 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?

Explicitly states when to use it (days used/left, planned-trip overstay) and when not to (non-Schengen countries, EU/EEA/Swiss passport holders, to whom the rule does not apply). The exclusions are concrete and actionable, not implied.

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