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

Annotations already declare readOnly/idempotent/non-destructive, but the description adds substantial behavioral context beyond them: error semantics that are never charged, the fact that an empty list with qualifie:false is a valid charged answer, the payment model ($0.01 via x402) and that no account/API key is needed. This is exactly the extra operational context annotations cannot carry.

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?

Although it is a dense paragraph, it is front-loaded with purpose, then usage, then error/payment semantics. Every sentence carries distinct operational information (validity flag, sibling routing, charge rules) with no filler.

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?

With no output schema, the description compensates by describing the return contents (domains, certifying body, start/end dates, current validity, rge.qualifie). Combined with error and payment behavior, an agent has everything needed to call and interpret the tool correctly.

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 the siret format is already documented. The description goes beyond it by telling the agent where to source the value (rechercher_entreprise's siret, verifier_entreprise's entreprise.siege.siret), which adds real routing value rather than restating 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 verb and resource ('List the RGE ... certifications of ONE French establishment') scoped by 14-digit SIRET and sourced from the official ADEME list. It explicitly contrasts itself with verifier_entreprise (whole company/SIREN, boolean label only), so an agent can distinguish it from siblings without opening schemas.

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 the decision context (check a contractor before subsidy-eligible renovation work) and names the alternative plus the condition that selects it (verifier_entreprise works on SIREN and only reports label existence). It also routes the agent to where the required SIRET comes from in sibling tools.

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