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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), and the description adds materially beyond them: billing reads cost 0, an API key is required (Authorization: Bearer), the billing:read scope, and the data provenance (Fonciq's own pull log rather than a portal statement). It stops short of describing response shape, which leaves a small gap.

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 core statement is front-loaded and useful, but the text is fully duplicated in French, and the cost paragraph is repeated verbatim in both languages ("Billing reads cost 0" / "Les lectures de facturation coûtent 0"). Roughly half the characters carry no new information.

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 read-only, no-required-param tool with 100% schema coverage and no output schema, the description supplies the scope, auth requirement, cost, data source and an explicit negative disambiguation. The only unstated element is what the response entries look like, which matters less without an output schema.

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 coverage is 100%, so `from`, `to` and `rf_account_id` are already documented with formats and the omit-for-default behavior. The description only restates the per-account/per-period framing and adds no format or edge-case detail beyond the schema.

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?

States a specific endpoint and resource: estimated Registre foncier fees per connected account for a period, and explicitly excludes the nearest misinterpretation ("Not Fonciq platform billing"), which differentiates it from the sibling billing_usage. An agent can identify the tool without opening the schema.

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?

Gives clear context for use — internal Fonciq pull log, no portal statement is read, per-account and per-period scope — plus the required scope (billing:read). It never names an alternative sibling or states when-not to use it, so the routing signal is implied rather than explicit.

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