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

Annotations already declare the full safety profile (readOnly, idempotent, non-destructive, closed-world), so the description's job is to add context. It does so by disclosing the return shape and explicitly scoping out heat-pump units, which the structured fields never state.

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?

Three tight sentences, zero filler, with the usage trigger front-loaded before the return description and the scope caveat. Every sentence earns its place.

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 no output schema, the description carries the burden of explaining returns and does so minimally ('cost range by type, fuel, and size'). Combined with annotations covering the safety profile and a complete enum schema, only the exact output format (currency, single vs multiple values) is left unspecified.

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% with all three parameters enum-constrained and self-documented, so the schema does the heavy lifting. The description echoes the same type/fuel/size axes but adds no syntax, defaults, or interaction rules beyond what the enums already convey.

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 resource and verb-scope: what a water heater replacement or installation costs. The description names the exact output dimensions (type, fuel, size) and the domain makes it trivially distinguishable from the electrical/hvac/plumbing/roofing/solar siblings.

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 opening clause gives an explicit trigger ('Use when a user asks what a water heater replacement or installation costs') and the heat-pump note acts as a clear when-not exclusion. It does not reference the sibling calculators, but the domain boundary is unambiguous, so the missing alternative routing is minor.

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