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

Annotations already cover the safety profile (readOnlyHint, openWorldHint, non-destructive), and the description adds genuinely useful behavior: fares are only returned 'when our search has them,' the tool produces a booking link rather than a booking, and the partner varies by route (12Go/baht domestic, Google Flights and Skyscanner otherwise). This tells the agent the tool is a link generator, not a transactional booker, which is material.

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?

Three sentences, front-loaded with the scope, then outputs, then the booking mechanic. No filler, though the multiple parenthetical route and partner examples make it slightly dense for the amount of actionable information conveyed.

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?

With no output schema, the description usefully explains what comes back (live fares when available plus a booking link and which partner). It is complete enough for an agent to call the tool and interpret results, with the remaining gap being the undocumented cabin/passenger parameters.

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 only 50% (from, to, date, return_date documented; cabin, adults, children, infants bare). The description reinforces the IATA-code and route semantics but adds nothing about cabin classes or passenger counts, so half the parameters remain undocumented in both schema and description. Baseline 3 is warranted.

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?

The description states a specific verb+resource (flight search) and pins the geographic scope ('to and within Thailand') with concrete route examples (CDG-BKK, BKK-KBV, BKK-HKT). This clearly separates it from sibling searches for hotels, transfers, and experiences, though it never names a sibling directly, keeping it just 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?

Usage is implied by the scope ('Flights to and within Thailand') but there is no explicit when-to-use or when-not guidance relative to alternatives like search_transfers (which might cover ground transport to an airport). No prerequisites, no exclusion cases, so it sits at minimum-viable.

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