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

The annotations already declare this as a read-only, idempotent, closed-world operation, so the safety profile is covered. The description adds the useful scope caveats that the result is indicative and excludes insurance and fees, but says nothing about precision, rounding, or whether the rate is applied monthly vs annually.

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 well-formed sentence with no filler, and the key qualifiers (indicative, excluding insurance and fees) are front-loaded. It is compact without being cryptic.

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 three-parameter, deterministic calculation with full schema coverage and no output schema, the definition states what is computed and what is out of scope. Only the return shape (single payment vs payment plus total interest) is left slightly ambiguous, though 'la mensualité et les intérêts' implies both.

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?

With 100% schema description coverage, the schema already documents principal in euros to the cent, the integer year range, and the nominal annual rate as a percentage that is not a TAEG. The description adds only the fixed-rate assumption, so it neither compensates for nor extends the schema meaningfully.

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 names a concrete computation (monthly payment plus interest) on a specific resource type (fixed-rate amortizing loan) and bounds the scope (excludes insurance and fees). It does not, however, distinguish itself from the sibling calculate_amortization, which an agent could easily confuse with it.

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?

There is no guidance on when to prefer this tool over calculate_amortization or the simulators listed as siblings. The only usage signal is implicit: it computes a payment rather than a full schedule, which the agent must infer.

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