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

Annotations already indicate a safe read-only operation, so the description adds meaningful behavioral context beyond them: it targets the statement closing date rather than the payment due date, explains the Canadian bureau reporting rationale, and states 'Deterministic arithmetic — same inputs, same answer.' No contradiction with annotations.

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 sentences, zero filler. The key output is front-loaded, then the critical date nuance, then usage triggers, then determinism. Every sentence carries distinct, necessary 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?

The description is complete for a tool with a rich output schema, full parameter documentation, and annotations covering safety. It explains the purpose, the main usage scenarios, a subtle date behavior, and the deterministic nature of the computation, leaving no operationally critical gap for an agent selecting or invoking 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?

Schema description coverage is 100%, so the schema already fully documents every parameter. The description adds only high-level semantic framing ('which card, how much, and by which date') and clarifies the importance of the closing date, but it does not need to compensate for missing parameter docs.

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, actionable result: 'The single highest-priority credit action right now: which card, how much, and by which date.' It clearly identifies the resource (credit action) and the verb (determine/select), and differentiates the tool from other planning tools by focusing on the single next step rather than a broader plan.

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 description explicitly tells an agent when to invoke the tool: 'Use this when someone asks what to pay, what to do first, or how to lower utilization before it is reported.' It gives clear contextual triggers, though it does not explicitly list sibling tools to avoid or state when not to use it.

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