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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the safety profile is covered. The description adds genuine behavioral detail beyond that: the exact formula used, the default assumptions (1500 sq ft, 50% high, 9/18 sq in per unit) and that vent counts are rounded up. It doesn't discuss units-in vs units-out edge cases, but it goes well past the annotation baseline.

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-loads the core purpose ('How much attic ventilation you need...') before the formula, and the formula block is compact and sequenced logically. It is dense but each sentence carries information; no filler.

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, so the description must convey return values, and it does — intake NFA, exhaust NFA, and vent counts. For a pure calculator with fully-described inputs and annotations covering safety, the definition gives the agent everything needed to invoke and interpret it, with only minor omission of output formatting details.

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 baseline is 3, but the description's formula adds real meaning beyond the schema: it ties attic_floor_sqft, ratio, upper_pct, and the two NFA-per-unit fields directly into the computation and the ceiling rounding of the vent count. This clarifies how each parameter is consumed, exceeding the schema's per-field descriptions.

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 verb and resource — computing attic ventilation net free area and vent counts under the 1/150 and 1/300 rules — and describes exactly what it splits into (intake vs exhaust) and returns (vent counts). It is clearly distinguishable from the many other calc_* siblings, which each cover a different material or quantity.

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?

Explains the condition that selects the rules — 1/300 as the 'balanced exception' requiring 40–50% high — which tells the agent when to use each ratio. It does not name alternatives or state exclusions, but given the tool is a single-purpose calculator with no overlapping sibling, clear conditional guidance is sufficient for a 4.

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