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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so safety is covered. The description adds genuinely new behavior: it discloses that the tool returns a cost range rather than a point estimate, and that heat-pump units fall outside the model — a real limitation an agent must know.

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: trigger condition first, return shape second, scope caveat last. Every sentence earns its place and nothing is padded.

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 usefully states the return is a cost range, and it flags the heat-pump gap. It is complete enough to call correctly, though it could say more about the cost-range format (e.g., low/high bounds) given the absent output schema.

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% and each parameter has an enum with its own description, so the schema carries the parameter documentation. The description's "by type, fuel, and size" only restates the fields without adding format or interaction rules, matching the baseline 3.

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 uses a specific verb and resource — it returns a cost range for water heater replacement/installation — and scopes the result by type, fuel, and size. This clearly separates it from the electrical, HVAC, plumbing, roofing, and solar calculators.

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 when a user asks what a water heater replacement or installation costs" gives an explicit trigger, and the note that heat-pump water heaters are not modeled is a useful scope exclusion. It stops short of naming an alternative tool for the excluded case, so it's not a full 5.

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