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

Annotations already declare readOnlyHint=true, destructiveHint=false, openWorldHint=false, so safety is covered; the description goes further by disclosing that it is FREE with no API key and 0 units, that it returns JSON rather than a drawing, and that dimensions are in millimetres. It also explains the failure mode it prevents (openings.z misuse, storeys without windows), which is genuinely useful context beyond the annotations.

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?

Front-loaded with the WHEN directive and organized under clear headers (WHY IT MATTERS, GOOD CALL, DO NOT), so an agent can skim it. It is somewhat long and repetitive between the schema enum text and the GOOD CALL examples, which keeps it just under the top mark.

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?

There is no output schema, but the description compensates by explaining that the return is JSON containing the scene plus the ordered next calls, and it names the downstream tools (cao_verifier, cao_pdf, cao_generer_dxf, cao_generer_ifc). Nothing needed to invoke and chain the call is missing.

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 description coverage is 100% and the enum already documents all three values, so the schema carries the parameter burden. The description largely restates the enum meanings (house / flat / veranda) rather than adding syntax or constraints, so the baseline 3 is appropriate.

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 action (return a complete, pre-verified example building scene as JSON) and explicitly contrasts it with the sibling cao_verifier. The described output ('hands back a COMPLETE, ALREADY-VERIFIED scene plus the exact next calls in order') is concrete enough for an agent to know exactly what it gets.

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 WHEN clause ('about to draw ANY French building for the first time...'), a GOOD CALL section naming three concrete invocations, and a DO NOT section that names the alternative (cao_verifier) for the check case. Nothing about routing is left to inference.

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