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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false, and openWorldHint=false, so the agent knows this is a pure, side-effect-free computation. The description adds nothing beyond that — no stated assumptions (e.g., that the efficiency factor is a loss allowance), no units caveat, no indication that the result is an estimate rather than a guaranteed yield. With annotations carrying the safety profile, a 3 is the right level.

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 with the core purpose front-loaded and no padding. The second sentence is a light cross-reference whose relevance is marginal, which keeps it just below a perfect score.

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?

An output schema exists, so return values need not be described, and annotations cover the safety profile; the schema fully documents all three inputs. For a simple two-required-parameter estimation tool, the definition is essentially sufficient, with only stated estimation assumptions 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%: roof_area_m2, annual_rainfall_mm, and efficiency_pct (default 80%, 0-100 bounds) are all documented in the schema itself. The description does not restate or add format/semantic nuance for any parameter, so the baseline of 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 first sentence names a specific verb and resource: 'Estimate annual rainwater collection volume from a roof.' That is unambiguous and distinguishes it from generic siblings like calculate_volume or calculate_area. However, it does not contrast itself with the closest neighbours (calculate_roof_area, calculate_garden_water_needs), so it stops short of a 5.

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?

Use case is implied by the purpose statement (sizing a rainwater harvesting setup from roof area and rainfall), but there is no explicit when-to-use, when-not-to-use, or prerequisite guidance. The only routing sentence points at list_bundles for a calculator bundle, which is navigation rather than selection guidance between sibling tools.

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