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

Annotations already declare readOnlyHint=true and idempotentHint=true, so the safety profile is covered. The description adds meaningful context by stating 'Résultat ESTIMÉ' and citing the standard financial method (TRI/XIRR vs CAGR) and that assumptions are caller-provided. This goes beyond the annotations and clarifies the nature of the output.

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 about three sentences and front-loads the core purpose. It repeats the title but uses a dash to integrate it. It is efficient and free of fluff, though slightly verbose in explaining the TRI/CAGR distinction. Overall well-structured for quick reading.

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 read-only, idempotent annotations and the 100% parameter schema coverage, the description is mostly complete. It specifies the returned value (true TRI) and the estimation nature. However, it does not describe the exact output format (e.g., whether only a number or an object with additional fields), but for a calculator tool this is a minor gap.

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% (each parameter has a French description). The description adds no parameter-specific details beyond what the schema already provides, such as 'versements programmés' which is implied by the parameter names. Baseline 3 is appropriate because the schema does the heavy lifting.

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 verb 'Calcule' and the resource 'rentabilité d'un placement à versements programmés', and explicitly distinguishes the true TRI (weighted by timing) from CAGR. It also specifies the returned value is the true TRI, making the purpose unambiguous and differentiating it from simple CAGR calculations.

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 provides no guidance on when to use this tool versus sibling simulators (e.g., simulateurs_scpi, simulateurs_private_equity). It does not mention alternatives, exclusions, or prerequisites. An agent would have to infer that it applies to general scheduled-payment investments, but no explicit routing is given.

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