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

Annotations already convey readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description adds genuinely useful behavior beyond annotations: entry and exit days both count, overlapping trips are de-duplicated, and the exact output items (days used, days remaining, compliance flag, first overstay date) are spelled out. No contradiction with annotations.

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 sentences with zero filler: purpose and rule in the first, counting nuances in the second, return-value summary in the third. The most decision-relevant information (what rule is checked) is front-loaded, and every sentence earns its place.

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 full schema parameter coverage, an output schema, and annotations covering safety/idempotency, the description only needed to explain edge-case behavior and result meaning — which it does. An agent knows what inputs to provide, what computation will be performed, and what the response will contain. Nothing material is missing.

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 each parameter (trips, plannedEntry, referenceDate) is already documented inline with formats and semantics; the description adds no parameter-level information beyond the rule mechanics that map to the trips field. Baseline 3 is correct here because the schema carries the heavy lifting.

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?

Description opens with a specific verb-resource pair ('Validate a set of trips against the Schengen Area rule') and concretely defines the rule (90 days in any rolling 180-day window). This cleanly separates it from siblings like check_residency, check_travel_residency, and find_nomad_visas, which deal with different constructs (residency status, visa discovery), so an agent can select it without opening sibling 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?

The domain context is explicit: this is the tool for compliance-checking trip itineraries against the Schengen 90/180-day rule. It does not name alternatives or state when-not-to-use conditions, but the rule specificity makes the intended selection obvious among the residency/tax/visa siblings. Lacks the explicit exclusion language that would earn a 5.

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