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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is fully covered without the description. The description adds one implied behavioral detail – that the tool sizes a 'tank' (not tankless) – but says nothing about assumptions, units of the result, or whether output is a recommendation range.

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 short sentences, front-loaded with the core action and no filler. The trailing list_bundles cross-reference is tangential to invoking this tool, which keeps it just short of a 5.

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 an output schema present, return values need not be explained, and both parameters are fully documented at the schema level. The remaining gap is context the schema cannot carry – the units of the recommended tank size and the tank-type assumption – which leaves the agent slightly under-informed.

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%; both parameters carry their own descriptions, including per-person litre figures for each enum value. The description adds no parameter-level meaning beyond what the schema already states, so the 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?

Specific verb plus resource ('Calculate recommended water heater tank size for a household') that an agent can match against the query 'what size water heater do I need'. It does not name any sibling or scope boundary, although the resource is inherently unique among the sibling list, so differentiation is largely handled by the name itself.

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 description gives no when-to-use vs when-not-to-use guidance, no prerequisites, and no statement of assumptions (e.g. tank vs tankless). The only routing signal is a pointer to list_bundles for related 'plomberie' calculators, which is discovery assistance rather than usage guidance.

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