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

Goes well beyond the readOnly/idempotent annotations: states fares are whole-trip totals for the whole party, that data is historical rather than live, that `provisional` rows have a high-biased minimum, and that only aggregates are published. This is exactly the kind of caveat an agent must know before presenting numbers to a user.

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 purpose, then return shape, then caveats — a logical order with no filler sentences. The sentence enumerating return fields is somewhat redundant given an output schema exists, which trims a point but not the practical value.

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?

Covers data provenance, aggregation level, and the provisional-data trap thoroughly, and the output schema handles return structure. The gap is the zero-required-parameter design: the description never says what happens when origin/destination/depart_month are omitted, nor how results are ordered or capped by `limit`.

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 58%, so roughly half the 12 parameters are documented structurally. The description adds real meaning for party sizing ('whole-trip totals for the whole party') and for the provisional flag ('minimum is biased high'), but says nothing about cabin, trip_type, stay_nights, limit, or max_price_usd beyond what the schema already states.

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?

Specific verb and resource with explicit bidirectional geography: 'Find observed round-trip fares from European hubs into Southeast Asian cities.' The scope constraint (Europe→SE Asia, fare aggregates only) plus the title cleanly separates it from the non-flight siblings (search_lodging, search_restaurants, compare_city_costs).

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?

Provides a strong exclusion — 'historical observations, not live availability' and 'no itinerary-level fares or booking links' — which tells the agent not to treat results as bookable prices. However, it never names an alternative source for live fares or explains when to prefer this over a sibling tool, so no explicit routing guidance.

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