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

Beyond the annotations, the description discloses two things the hints do not: the required OAuth 'trips' scope and that the endpoint is rate-limited — exactly the auth and throttle context an agent needs before calling. It does not address the non-idempotent behavior flagged by idempotentHint=false (e.g. repeated calls sending repeated emails), leaving one behavioral gap.

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?

Four short sentences, front-loaded with the action before the constraints, and zero filler. The somewhat telegraphic style still parses cleanly and every clause carries information.

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?

An output schema exists, so return values need not be explained, and the description covers side effects, auth scope, rate limits, and the key exclusion. What remains unstated — that repeat invocations send repeat emails — is the only meaningful omission for a five-parameter, externally-visible operation.

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 all five parameters (including the optional email, locale, firstName, lastName) are already documented in the schema. The description adds no parameter-level detail beyond referencing continue_url, so the baseline 3 applies.

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 ('Email continue_url (/s/{id})') and the destination ('to the verified account inbox'), so the agent knows exactly what the call does. It also distinguishes itself from create_booking via 'Not a booking', and cannot be confused with save_trip or get_trip.

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?

It gives an explicit when-not ('Not a booking') and an alternative path ('you can share continue_url without emailing'), which is strong routing guidance. It stops short of naming a positive trigger scenario or a sibling tool to prefer in a given case, so it is clear context rather than a full when/when-not map.

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