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

Annotations already declare readOnlyHint and openWorldHint, so safety is covered. The description adds real behavioral substance beyond that: it performs format checks, checksum verification, and an existence lookup against registered companies/establishments — the last of which explains why openWorldHint is set.

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?

Two sentences, no filler. The capability and accepted formats are front-loaded, and the usage cue is a short trailing sentence rather than padding.

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 one-parameter, read-only validate tool with no output schema, the description covers inputs, checks performed, and usage timing. It never indicates the shape of the result (e.g., pass/fail plus matched entity), which is the only meaningful gap.

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% and the single param is documented, so the baseline is 3. The description goes further by pinning each accepted identifier type to its exact length (9, 14, FR+11), which is more actionable than the schema's generic min/max bounds.

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?

Names a specific verb (validates) and the exact resource universe (SIREN 9 digits, SIRET 14 digits, intra-EU VAT FR+11), then enumerates what is verified. This clearly separates it from siblings like get_company or get_establishment, which retrieve rather than validate.

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?

"Use it first when an identifier was typed by a person" gives an explicit triggering condition and positions the tool ahead of retrieval siblings. It stops short of naming the alternative to call once validation passes (e.g., get_company), so it is clear context without full routing.

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