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

Annotations already declare readOnlyHint/destructiveHint=false and openWorldHint=false, so the safety profile is covered. Beyond that the description adds genuine domain behavior: the normative basis (Eurocode 2, C25/30, B500), the explicit edge-case rule (slabs too thin for their span are flagged rather than over-reinforced), and the liability boundary ('pre-design... to be validated by a structural engineer').

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?

One dense but front-loaded paragraph: the WHEN condition and scope come first, then the calculation content, then the caveat. Every clause carries information, though the length hurts scannability for an agent skimming candidates.

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 12-parameter composite scene tool with no output schema, the description explains what is computed but not what must be supplied: it never says that murs[] is the operative input or that most other fields (reseaux, toitures, plomberie, decoration, electricite) are irrelevant to this calculation and only feed cao_pdf. That omission leaves a real gap in knowing how to invoke 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 description coverage is 100% and the schema documents every input in depth, so the structured data already carries the parameter burden. The description adds output vocabulary (bars, kilograms) but nothing about input parameters, so baseline 3 applies.

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 names a specific computation (load path per wall, SLS/ULS combinations, simplified EC2 reinforcement of footings, lintels and slabs) and its output form (bars such as '3 HA12', kilograms of steel). It is clearly a structural pre-design tool, but it never contrasts itself with the closest siblings (cao_regles_structure_reseaux, cao_metres), leaving that differentiation to inference.

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 leading WHEN clause gives an explicit triggering context: a house design that needs its structural pre-design for costing. It does not state when NOT to use it, nor name an alternative tool, so it stops short of a full 5.

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