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

Annotations already cover read-only and open-world behavior, and the description adds real context beyond them: travel offers may accompany breaks, an offer with sponsored: true is a paid placement that must be presented as sponsored, and payment never alters the plan. Those are policy/disclosure obligations an agent could not infer from the schema, though pagination or rate-limit behavior is not mentioned.

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, front-loaded with the return payload before the offer/sponsorship caveat and the usage cue. Dense but each sentence carries information; the closing usage sentence could have been folded into the first without loss.

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?

Because an output schema exists, the description is not obliged to enumerate return fields, yet it covers the plan outputs, the adjacent travel-offer behavior, the sponsorship rule, and the call trigger. Nothing needed to invoke the tool correctly 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 every parameter (days, year, months, country) is already documented in the schema. The description only echoes the two required inputs ('Given a country and a number of leave days') without adding format or constraint detail, so the baseline of 3 is correct.

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 gives a specific verb and resource ('returns the breaks that give the most days off in a row, the exact dates to request as leave, the totals, and a link'), so an agent knows exactly what comes back. It implicitly separates itself from single-weekend siblings like find_long_weekends by framing the result as a year-long plan, but it never names a sibling explicitly, which keeps it short of a 5.

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?

It states clear trigger conditions: 'Use it when someone asks how to get the most time off from their holiday allowance, or to plan their vacation days for a year.' That is a genuine when-to-use clause, but there is no when-not guidance and no pointer to the alternative tools (find_long_weekends, start_planner) for adjacent requests.

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