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

Goes well beyond the readOnly/openWorld annotations: discloses per-call cost ($0.05 USDC via x402 on Base/Solana/Arc), that failed calls are not charged, that fares are for a single traveller, and that market drives the currency. This is exactly the payment and failure semantics an agent needs before invoking a paid read tool.

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 and return shape, then the optional filters, then the payment note. Dense but every clause carries information; the sentences run long, which slightly hurts scanability but not substance.

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?

An output schema exists, so return values need not be detailed, yet the description still sketches the response structure. Combined with scope, optional filters and payment terms, an agent has everything needed to call it 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 description coverage is 100%, so all eight parameters are already documented in the schema (IATA codes, date range, cabin values, limit 1-20, market currency). The description restates cabin, max stops and market's currency role without adding syntax or format beyond the schema, 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 resource and scope ('Flight fares for one route and date, one-way or round trip') and enumerates exactly what comes back: cheapest/fastest/cheapest-nonstop, then up to 20 itineraries sorted by price. No sibling covers flights, so there is nothing to confuse it with, and the verb 'fare search, not a booking' is unambiguous.

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?

Clearly positions the tool: a fare search rather than a booking, for a single traveller, with optional filters (cabin, max stops, market). It does not name an alternative tool or state exclusions, but with no flight sibling there is nothing to route against, leaving context clear.

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