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

Annotations already provide readOnly and idempotent hints; the description adds valuable behavioral details including the Luhn algorithm, automatic La Poste special case handling, input tolerance for spaces/dashes, and the exact return object shape. This exceeds what annotations convey.

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?

Five sentences, each conveying a distinct piece of information (purpose, structure, return value, use cases, special case) with no redundancy or filler. The most critical information is front-loaded.

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 description covers purpose, input format, output structure, algorithm, special case, and appropriate usage contexts. Despite lacking an output schema, the return value is explicitly described, making the tool fully self-contained.

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?

Although the schema already fully describes the single parameter with an example, the description adds semantic meaning by breaking down the SIRET into SIREN and establishment parts, enriching the understanding of what the parameter represents.

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 validates a French SIRET number using the official Luhn algorithm, which is specific and distinct from sibling validators like validate_iban or validate_nif. It also explains the SIRET structure, further clarifying the resource.

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?

Explicitly lists use cases (French invoices, supplier registrations, B2B transactions) which gives clear context. However, it does not mention when not to use this tool or explicitly reference alternatives among siblings, so it falls short of the highest bar.

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