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

Annotations declare readOnlyHint=false, destructiveHint=false, openWorldHint=false, so the agent already knows this creates local state without destroying anything. The description adds genuinely useful operational context the annotations lack: accepted formats, a 20 MB ceiling, base64 payload encoding, the returned plan_id, and that the call is Free (relevant given the credit-oriented siblings).

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?

Three short sentences with zero filler, ordered as use-case, mechanism/return, then exclusion, with the cost signal ('Free.') packed into a single word. Every sentence carries distinct information.

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 naming the return payload (plan_id, dimensions, features). Combined with formats, size limit, exclusions, and cost, an agent has everything needed to invoke it correctly without further lookup.

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 both parameters are already documented and 3 would be the baseline. The description still adds meaning beyond the schema: which file formats contenu_base64 may carry and the 20 MB size limit, which are constraints neither the schema nor its French examples convey.

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?

Specific verb+resource: uploads a technical drawing of a manufactured part and returns a plan_id plus parsed dimensions and features. The accepted formats (PDF, DXF, STEP) and the costing intent distinguish it from siblings like chiffrer_piece and verifier_devis, which operate downstream on the resulting plan.

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?

Explicit trigger ('when the user provides a technical drawing ... that will be costed') and explicit exclusions ('Do not use for photos, invoices or documents that are not part drawings'). It stops short of naming a specific sibling as the alternative path, so it is clear context rather than full when/when-not/alternatives routing.

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