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

The description goes well beyond the annotations by explaining that the traveler completes sign-in, price review, house rules review, cancellation policy review, and payment in the external checkout flow. It explicitly discloses that no reservation or charge occurs and warns never to pass card details, which is valuable safety context that the annotations do not convey.

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 front-loaded sentences with no waste. The most important constraint, that this is only a checkout link and not a reservation or charge, appears immediately after the core action.

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?

There is no output schema, but the description names the return value (checkout_url) and explains the downstream flow the traveler will see. Combined with the safety disclosures, an agent has everything needed to call the tool 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 coverage is 100%, so the schema already documents quote_id as coming from get_quote with a 15-minute lifetime. The description adds meaning by clarifying that the tool checks whether the quote is still available, not merely that it accepts the ID.

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 precise verb and outcome: it checks that a quote_id is still available and returns a checkout_url. It explicitly distinguishes this from an actual booking by saying the tool "reserves nothing and charges nothing by itself," which resolves the ambiguity in the name "book."

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: call it with a quote_id from get_quote when a traveler wants a checkout link. However, the description never names alternatives or states when not to use it, such as what to do if the quote has expired or whether find_cheaper should be consulted first.

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