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

Annotations already cover the safety profile (readOnlyHint, destructiveHint=false, openWorldHint), so the description's added value is provenance and reliability: data comes from a cache of user-found fares from recent days and prices are explicitly approximate. That is exactly the kind of behavioral context annotations cannot express. Minor gap: nothing about result caps via limit or what an empty result looks like.

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 compact sentences ordered by importance: what it is, the no-destination variant, the accuracy caveat with the alternative, then use cases. Zero filler and no repetition of the annotations.

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 an 8-parameter read-only lookup with no output schema, the description covers everything an agent needs to call it correctly: accepted date granularity, the two modes, approximate pricing, and the route to a precise alternative. Remaining per-parameter details are adequately carried by the schema.

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 75%, so the schema already carries most parameter meaning. The description adds real semantics beyond it by explaining that omitting destination switches the tool into a destination-ranking mode — a behavioral effect the schema only hints at via 'для подборки направлений'. It leaves direct_only (no schema description) and limit unaddressed.

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 — cached minimum prices from LastBilet for a date or month — and immediately explains the two operating modes (with destination = route price, without destination = 'where to fly cheaply' ranking). It also explicitly contrasts itself with search_flights for exact/baggage-inclusive prices, so an agent can distinguish it from siblings without opening a schema.

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?

Gives clear when-to-use triggers ('гибких дат, бюджета, вдохновения') and an explicit alternative for the exact-price case ('точные и с багажом даст search_flights'). It does not differentiate from price_calendar, which is arguably the closest sibling for date-flexible browsing, and gives no guidance on when the cached data is too stale to trust.

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