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

Annotations already indicate a safe, closed read operation, and the description adds important behavioral context: it is a paid x402 tool costing $0.001 USDC on Base, an unpaid call returns PaymentRequired, and retry requires _meta["x402/payment"]. This is exactly the kind of operational detail an agent needs before invoking it.

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?

The description is a compact single paragraph that front-loads the purpose, then explains the payment requirement, then gives an example. Every sentence carries useful information for an agent deciding whether and how to call the tool.

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 a simple read-only calculator with full schema coverage and annotations, the invocation details are essentially complete. The main missing piece is that no output schema exists and the description does not say what the return value looks like, though this is a minor gap for a straightforward GST calculation.

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 coverage is 100%, so the schema already documents both parameters. The description still adds value by clarifying that mode accepts 'exclusive or inclusive' and by showing a complete argument object, although it does not explain the amount format or rounding behavior beyond the schema example.

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 exactly what the tool computes: NZ GST at 15%, with exclusive or inclusive modes. This is specific enough to distinguish it from the sibling validation and working-day tools without opening 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 description implies the tool is used for GST calculation and shows example arguments, but it does not explicitly say when to use it versus alternatives or when not to use it. Since the sibling tools serve unrelated validation/date purposes, the gap is mild but still present.

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