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

The annotations already declare readOnlyHint and idempotentHint, so the description doesn't need to restate that. It adds the behavioral constraint that this is an ordinary annuity with payments at period end, and clarifies that the rate is per-period in percent, which prevents misuse. 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?

The description is a single concise sentence that front-loads the core purpose and includes the key nuance about payment timing. Every word earns its place.

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 simplicity of the tool, the combination of the description, full schema descriptions, and annotations is sufficient. The description covers the main concept and the rate unit, leaving no obvious gaps for a straightforward financial calculation. It doesn't explain the formula, but that's not required.

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?

The input schema already provides descriptions for all three parameters (payment, periods, ratePct), and the description reinforces that ratePct is per-period and in percent. However, it adds little beyond the schema's existing parameter descriptions, so the added semantic value is marginal.

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 explicitly states the tool calculates the present value of an ordinary annuity, with a parenthetical clarifying level payments at period end. This clearly distinguishes it from sibling tools like annuity-fv or annuity-payment.

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 when to use the tool by defining the scenario (ordinary annuity, period-end payments), but it does not explicitly name alternatives or state when not to use it. It doesn't mention that annuity-fv handles future value or that present-value may handle general cash flows. Guidance is implied rather than direct.

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