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

Annotations cover the safety profile (not read-only, idempotent, non-destructive), and the description adds real context beyond them: the change only applies to an unconfirmed/open booking, the already-sent link keeps working so nothing new is dispatched, and only trip-listed options are accepted. Those are exactly the side-effect and precondition details an agent needs before mutating state.

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-loads the situation, then the action, then the side effects, in roughly three sentences with no filler. The trailing fragment 'Only an option the trip lists as available' is slightly clipped, but it still earns its place as a validity rule.

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 two-parameter mutation with annotations and no output schema, the description covers trigger, precondition, side effects and option validity. The remaining gaps — what taskId actually identifies and what happens when an unavailable option is supplied — keep it from being complete.

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 0%, so the description carries the burden: it explains paymentOption's meaning and restricts it to trip-available values, which reinforces the enum. However, taskId is never explained — an agent cannot tell whether it is a booking id, a trip id or a task handle — so half the input surface is still undocumented.

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: switches an open booking to a given paymentOption, with the precondition that it happens before confirmation. The clause about the existing link staying the same implicitly separates it from siblings like resend_link and send_to_payer, so an agent can pick it without opening the schema.

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?

Gives a clear trigger condition (traveller wants a different payment method before they have confirmed) and a validity constraint (only an option the trip lists as available). It does not name a named alternative or state explicitly when not to use it, so it stops short of the top band.

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