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

Annotations already indicate read-only, idempotent, and non-destructive behavior, and the description adds valuable context: 'does not make payments, change accounts, fetch external data, or retain tool inputs.' It also explains the utilization-versus-rate trade-off, setting accurate expectations for the kind of answer returned.

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?

Every sentence earns its place: trigger, output shape, trade-off rationale, and boundary statements. The description is information-dense without repeating schema details, and the most decision-relevant information is front-loaded.

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?

Given the rich input schema, existing output schema, and annotations covering safety and side effects, the description supplies the missing selection and expectation-setting context. An agent has everything needed to decide when to invoke it and what to expect back.

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%, and every parameter already has detailed documentation in the input schema. The description refers to 'the amount given' and 'supplied figures' but adds no parameter-level meaning beyond what the schema provides, so the baseline of 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?

The description opens with an explicit trigger—'Use this when someone asks which card to put a purchase on'—and names concrete outputs: the card with least utilization impact, the cheapest card to carry, and the trade-off when they differ. This clearly defines the tool's verb, resource, and purpose, and distinguishes it from sibling planning/explanation tools.

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 states a clear usage trigger('someone asks which card to put a purchase on') and scope ('Calculates scenarios from supplied figures'). It does not explicitly name alternative sibling tools or say when not to use this tool, so it falls just short of full exclusionary guidance.

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