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

Annotations already declare destructiveHint=true and idempotentHint=true, so the safety profile is covered. The description adds genuinely non-obvious behavior: this is a full replacement, not a patch — 'send the whole checkout again' warns the agent that omitted fields are lost. It does not say what happens on a paid/expired session or what is returned.

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 filler, with the mutation and its precondition front-loaded before the resubmission rule. Every clause carries information the agent needs.

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?

For a destructive, idempotent mutation with a fully documented nested schema, the description covers scope, precondition, and replacement semantics. The one gap is that no output schema exists and the description never says what the call returns (presumably the updated checkout), leaving the response shape to inference.

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% and the nested checkout object is thoroughly documented, so the schema carries the parameter burden. The description only adds the whole-body-resubmission convention and the 'as for create_checkout' shape equivalence, which is marginal beyond the schema.

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: replace the content of an unpaid checkout session, enumerating the mutable dimensions (trip, motorcycles, riders, buyer). It implicitly separates itself from create_checkout by scoping to an existing 'unpaid' session, though it never names the sibling explicitly.

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 one real precondition — the session must be unpaid — which tells the agent when this tool applies. It gives no guidance on the create_checkout vs update_checkout vs get_checkout decision path, nor on what to do when the session is already paid or expired.

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