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

Beyond the readOnlyHint and openWorldHint annotations, the description discloses important behavior: pricing of $0.002 USDC per successful call via x402, that failed calls are not charged, that calculations use exact cents with no outside source, and that outputs are capped at 600 months and 200 cashflows. These are material operational details an agent needs before invoking a paid tool.

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 dense but well-structured, front-loading the tool's purpose and then using mode-labeled clauses to cover each calculation path. It includes pricing and failure behavior without unnecessary repetition, and the length is proportionate to a seven-parameter multi-mode paid calculator.

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?

An output schema exists, so the description does not need to explain return values. Given that, the description covers the essential context: all four modes, their inputs and constraints, exact-cent behavior, rate and term limits, and payment/failure semantics, leaving no major gap for correct invocation.

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 all seven parameters. The description still adds cross-parameter meaning by explaining rate ranges and annual versus per-period interpretation, that cashflows start at time 0 and are capped at 200, and that terms are limited to 50 years or 600 months.

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 financial calculator resource and enumerates its four modes: annuity, compound, npv, and irr. It also distinguishes the tool with exact-cent calculations and no outside source, giving an agent a clear sense of what it does beyond generic arithmetic or units conversion.

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 explains what each mode computes, including monthly payment/amortisation for annuity, future value for compound, and discount/IRR for cashflows. This supports mode selection, but it does not explicitly state when not to use the tool or name sibling alternatives, so it falls short of a full 5.

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