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

Annotations already declare readOnlyHint, openWorldHint false, and idempotentHint, covering the safety and repeatability profile. The description adds useful behavioral context by emphasizing that the rate is per period and that the payment is level (fully amortizing), which goes beyond the schema. 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?

A single, straightforward sentence with no wasted words. It front-loads the core purpose and includes a helpful clarification about the rate.

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 tool has a full schema, output schema, and annotations, so the description does not need to explain return values or safety. It adequately covers the calculation purpose and rate semantics, making it sufficiently complete for a simple financial formula tool.

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 baseline is 3. The description's note that 'rate is per period' reinforces the schema's 'Rate per period in percent' but does not add new semantic meaning beyond what the schema already provides.

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 clearly states the tool computes the level payment that amortizes a present value over n periods, using the loan-payment formula. This specific verb and resource distinguish it from sibling tools like annuity-fv and annuity-pv, which calculate future/present value rather than the 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 gives clear context: it is the loan-payment formula with a per-period rate, implying when to use it. However, it does not explicitly name alternative tools or provide exclusion criteria, so it stops short of a 5.

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