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

No annotations are provided, so the description carries the full burden of disclosure. It covers the essential behaviors: pure format validation, no external label lookup, and critically the $0.01 USDC Base x402 payment cost — a material side effect an agent must know before calling. It does not mention error behavior on invalid input, but for a simple check tool this is adequate.

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 front-loaded sentence with zero filler. Every clause earns its place: the purpose, the format spec, the no-lookup limitation, and the payment disclosure. Model-efficient and complete.

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 simple format-check tool with no output schema, the description covers purpose, input format, scope limitations, and cost. The main gap is the unspecified input-passing mechanism given the permissive additionalProperties schema, and the absence of any hint about the return value (boolean vs. error). Minor given the tool's simplicity.

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?

There are 0 defined parameters, giving a baseline of 4. However, the schema sets additionalProperties: true, meaning arbitrary key-value pairs are accepted, and the description never explains what key or format to use to pass the code to validate. The format pattern (4 digits + letter) partially clarifies the expected value, but the input mechanism remains ambiguous.

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 verb+resource: 'format check' of 'French APE/NAF rev.2' with an exact format pattern (4 digits + 1 letter, e.g. 62.01Z). This clearly distinguishes it from siblings like check_siret and check_iban, which validate different code types. The scope is unambiguous.

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 'No INSEE lookup of the label' clause implies the tool is for structural validation only, not for retrieving semantic label data — which is useful scoping. However, no explicit when-to-use guidance or named alternative is provided, so routing relies on inference from the sibling list rather than direct instruction.

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