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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the safety profile is covered. The description still adds genuinely non-obvious behavior: trips are 'processed in memory and not stored', which is a privacy guarantee an agent cannot infer from the schema or annotations, plus the not-legal-advice boundary.

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 tight sentences with zero filler; the primary output is front-loaded and the two secondary clauses (in-memory processing, non-legal-advice) each carry distinct value. Nothing could be cut without losing information.

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 compensates by naming both return values (earliest re-entry date, longest stay), and annotations cover the safety profile. Minor gap: it doesn't characterize inputs (max 100 trips, minimum one, the 90/180-day rule basis) or behavior on malformed/overlapping trips, though the schema covers most of that.

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 both parameters (trips, referenceDate) are already documented with format and inclusivity rules in the schema. The description adds only that trips must be 'explicitly provided in this request' — a scoping note, not new parameter semantics. Baseline 3 applies when the schema does 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?

The description states a specific verb and two concrete outputs: the earliest legal re-entry date and the longest consecutive stay. It is immediately distinguishable from etias_check and schengen_check_days by its forward-looking planning intent, though it never names either sibling explicitly.

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 context is implied by 'from trips explicitly provided in this request' and the 'planning only' framing, which tells the agent this is a planning aid rather than a compliance check. However, it never states when to prefer it over schengen_check_days or etias_check, which are the obvious alternatives an agent would weigh.

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