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

Annotations declare readOnlyHint=true and openWorldHint=false, so safety is covered. The description goes well beyond them by disclosing the USDA NRCS PA-1 capacity table source, the exact runoff formula, the adequacy condition (Q <= capacity at slope), the downspout-count formula, and the max-roof-area relation. It does not explicitly state the output shape, but the behavioral mechanics are unusually transparent.

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?

The purpose is front-loaded in the first sentence, followed by formulas that earn their place for a complex engineering calculation. No filler or repetition, though the formula block makes it a dense read compared to simpler tool descriptions.

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 7-parameter tool with no output schema, the description is nearly complete: it explains the computation, the adequacy criterion, and the max roof area. The main gap is that it never states the shape of the result (e.g., capacity, Q, adequacy boolean, downspout count), which an agent would have to infer.

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%, so all seven parameters are already documented with defaults in the schema. The description adds formula-level meaning by showing how roof area, rainfall intensity, slope, gutter capacity, run length, and max run per downspout feed into the calculation. That is useful added context, but it stops short of per-parameter semantics beyond what the schema already provides.

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 states a specific verb+resource: checking gutter runoff capacity in a design storm and computing the number of downspouts needed. This is clearly distinct from siblings like calc_roofing or calc_appliance_energy_cost. The agent can tell what the tool does without opening the schema.

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?

Usage context is implied by the design-storm scenario ('Check whether a gutter can carry the runoff from your roof in a design storm'), but there is no explicit when-to-use, when-not-to-use, or named alternative. In a large calculator suite this is adequate but leaves the agent to infer when this specific calculation applies versus other calc_* tools.

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