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

Annotations already declare the write/idempotency/destructive profile, and the description adds genuinely new context: the required auth scope, the exhaustive set of writable fields, and the operations that are explicitly out of reach. It reinforces rather than contradicts destructiveHint=false. It does not describe failure behavior or partial-update semantics.

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-loaded with the core action, then auth requirement, then allowed fields, then boundary exclusions. Every sentence carries information an agent needs, with no filler or repetition of the title.

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 an output schema present, annotations covering the safety profile, and 100% schema description coverage, the description fills the remaining gaps: auth scope, permitted fields, and destructive boundaries. Nothing needed to invoke it correctly is missing.

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 the baseline is 3, but the description adds value by enumerating the concrete allowed field names (currency, units, sourceAirportCode, passports, visas, lists.bookmarked, etc.) that the schema only gestures at with 'Only traveler profile fields are allowed.' It still leaves the operation enum semantics to 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?

The description names a specific verb and resource ('Update one saved traveler profile preference for the signed-in user') with a clear single-item scope. It is unambiguous and easily separated from the read-only sibling profile.preferences.get, though it never explicitly names or contrasts siblings.

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 clear preconditions (OAuth 2.0 token with profile.write scope) and explicit exclusions ('cannot delete the account, unlink messengers, or change email'), which is strong when/when-not guidance. It stops short of pointing to an alternative tool for those excluded operations.

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