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

Annotations already declare readOnly/idempotent/non-destructive, so the safety profile is covered. The description usefully adds freshness context ('fares are the cheapest Aviasales travellers found in the last 48 hours') and clarifies that returned prices are indicative, with the live price only on the booking page — valuable behavioral context beyond the 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?

Four sentences, front-loaded with the core purpose, but the second sentence largely restates the first ('cheap flights ... with the cheapest days to fly'), which is padding. The freshness and live-price notes in the last two sentences are the only content that 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?

For a read-only search tool with full annotation coverage and no output schema, the description covers purpose, data freshness, and the caveat that displayed fares are not the final booking price. It is missing explicit guidance on currency behavior and the from/to 'anywhere' semantics, but is otherwise sufficient to invoke correctly.

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 the schema already documents from, to, month, and country with examples. The description only loosely echoes the flexibility of 'from'/'to' ('any city', 'one place or anywhere') without adding format or edge-case detail, so baseline 3 applies.

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 opening sentence states a specific verb-less but clear objective: cheapest departure days for a route in a month, naming the resource (route/month) and the output (cheapest days). It does not, however, differentiate itself from siblings find_deals or look_up_place, so an agent must infer the boundary between 'cheapest dates' and 'deals'.

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 description never says when to use this tool versus find_deals or look_up_place, nor does it state required inputs such as needing a month. 'From any city, to one place or anywhere' implies breadth but gives no selection criteria or exclusions.

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