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

Annotations already declare readOnlyHint=true, destructiveHint=false, and openWorldHint=false, so the safety profile is covered elsewhere. The description adds genuinely new behavioral context: no charge is made, card numbers are never returned, buyer read access is required, and the OAuth scope/well-known endpoint is named. Only rate limits or failure modes are absent.

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?

Sentences are short and front-loaded, leading with the core read operation before caveats and auth details. The auth requirement is stated twice ('Requires buyer read access' / 'Requires sign-in with buyer access'), which is mild redundancy worth trimming.

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?

The tool is simple (zero params), annotations carry the safety hints, and an output schema exists so return values need no explanation. The description covers the auth/scope prerequisite, the no-charge and no-card-number guarantees, and the shape of the result, leaving nothing an agent needs before calling it.

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?

The tool takes zero parameters, so there is nothing for the description to disambiguate and the baseline is 4. The description correctly conveys that the call is parameter-free by framing the operation around the signed-in buyer's implicit identity.

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 ('Read whether the signed-in buyer has a card saved') plus the use case ('for in-chat checkout'), and adds the return payload ('the page where they can add one'). An agent can distinguish this from siblings like preview_checkout or confirm_purchase without consulting any 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?

The 'for in-chat checkout' framing gives clear context for when this is the right call, and 'Does not charge the card' implies it precedes, not replaces, a checkout tool. It stops short of naming an explicit alternative or stating when-not to use it, so it falls just short of a 5.

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