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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world). The description adds genuinely useful behavior the annotations cannot: fares are cached from what Aviasales travellers found in the last 48 hours, and the live price appears only on the booking page. That freshness caveat is exactly the kind of context an agent needs when reporting prices.

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?

Front-loaded with the core purpose, but the second sentence ('Cheap flights from any city, to one place or anywhere, with the cheapest days to fly') largely restates the first and the title. The price-freshness sentences do earn their place; the middle sentence does not.

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?

There is no output schema, so the description carries the burden of explaining returns. It implies a list of cheapest days but never states the shape (dates plus prices, currency, whether round-trip or one-way). Adequate but leaves an agent guessing about the response structure.

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 four parameters (from, to, month, country) are already documented in the schema, including the month format and the country-for-currency rule. The description adds no parameter-level detail beyond that, 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?

States a specific verb+resource: cheapest departure days for a route in a given month. An agent can tell it returns day-level pricing rather than actual itineraries. It does not explicitly differentiate from the sibling faredeals_find_deals, so it stops 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?

No when-to-use guidance, no prerequisites, and the sibling faredeals_find_deals and faredeals_look_up_place are never mentioned. The phrase 'from any city, to one place or anywhere' hints at flexibility but gives no routing rule for choosing this tool over its neighbours.

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