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

Annotations already establish readOnlyHint=true, destructiveHint=false, and openWorldHint=true, so the safety profile is covered. The description adds genuinely new behavioral context — results are indicative only and cannot be booked, and the comparison is bounded to 31 dates — which is the key trait an agent must know. It stops short of describing the response shape, but an output schema exists.

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?

Two sentences, zero waste. The capability and its bound come first, then the non-bookability caveat and the correct follow-up tool — the most decision-relevant information is front-loaded.

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?

Given a fully covered 13-parameter schema, rich annotations, and an output schema that documents the return values, the description supplies everything else an agent needs: what is compared, the date bound, that results are not bookable, and which sibling to call next.

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 every parameter including the one-way vs round-trip semantics of stay_days is already documented in the schema. The description adds no syntax, format, or constraint detail beyond that baseline.

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 and resource: 'Compare the lowest one-way or round-trip fare for each departure date across up to 31 dates.' The scope (per-date comparison, up to 31 dates, one-way or round-trip) makes it clearly distinguishable from the sibling search_flights.

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?

Explicitly routes the agent: 'Prices are not bookable; search the chosen date with search_flights.' It names the alternative tool and the condition under which it should be used, so the agent never mistakes this for a booking or single-date search.

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