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

Annotations already establish readOnly/idempotent/non-destructive/non-open-world, and the description is consistent with them. It adds genuine context beyond the annotations: the response shape ('use card X here, because Y, up to cap Z', a second-best card, caps/conditions, source link) and the data-coverage/currency limitation (Vietnam-issued cards, VND).

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?

Well front-loaded: the trigger condition comes first, followed by inputs and then the answer shape. It is a little long, and the detailed description of the return line partially duplicates what the output schema already provides, but no sentence is wasted.

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 an 8-parameter tool with nested objects and an existing output schema, the description covers the required inputs, the scope limits, and the nature of the answer. Optional parameters (picks, statement_spend, date, channel) are left to the schema, which is acceptable given its full coverage.

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 schema already documents every parameter including place, cards, currency and amount. The description largely echoes that ('place' as merchant/category/city, 'cards' by name or id) and adds only the minor nuance of combining place and category ('dining in Tokyo'). Baseline 3 is appropriate.

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: pick which of the user's cards to pay with, for maximum cashback. The name/title are clarified rather than restated, and there are no siblings to confuse it with.

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?

Opens with an explicit trigger ('Use this when someone asks which of their credit or debit cards to pay with at a shop, app, category or city'), and later bounds the tool with a scope exclusion ('covers Vietnam-issued cards'), so the agent knows both when to call it and when its answer is out of scope.

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