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

With no annotations provided, the description carries full responsibility for behavioral disclosure. It thoroughly explains the tool's actions: Luhn checksum validation, SIRENE registration check, VAT number computation, live VIES validation, and a fallback verdict if VIES is flaky. It also mentions 1h caching and the price per call, providing complete transparency.

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 packed with useful information in a compact form. Each sentence contributes value—purpose, query format, validation steps, output verdict, fallback behavior, caching, and pricing. It is slightly longer than strictly necessary but remains efficient and well-organized.

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 tool's moderate complexity and the absence of an output schema, the description is remarkably complete. It covers what the tool does, how to structure the query, what the response looks like (three possible verdicts), reliability caveats, caching, and cost. This is sufficient for an agent to confidently select and invoke the tool.

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?

The schema only defines a single string parameter 'number' with no description, so the description must compensate. It does so by explaining the accepted formats: SIREN (9 digits) or SIRET (14 digits), with concrete examples. This adds crucial semantic detail that the schema lacks.

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's purpose: a one-call compliance check for the French e-invoicing reform. It specifies the exact validation steps (Luhn checksum, SIRENE registry, VAT computation, VIES validation) and distinguishes itself from single-purpose siblings like validate_siret_fr and validate_vat_eu.

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 clear context for when to use this tool: for French e-invoicing compliance, especially after 2026-09-01 when SIREN becomes mandatory. It implies this is the go-to for a comprehensive check, though it does not explicitly state when not to use it or name alternatives.

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