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

Annotations already declare readOnlyHint=true, idempotentHint=true, openWorldHint=false, destructiveHint=false, so safety behavior is covered. The description adds return-shape context the annotations do not: a low/high cost range, regional context, and contractor comparison guidance. It stops short of noting the estimates are non-binding or currency assumptions.

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 sentences, zero filler, and the usage trigger is front-loaded ahead of the return-value summary. Nothing repeats the title or name.

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 read-only calculator with no output schema, the description does the necessary work by telling the agent what comes back (low/high range, regional context, contractor guidance). It omits caveats an agent might need to relay, such as estimate approximation or currency, so it is strong but not fully complete.

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 three of four parameters are enums with documented values, so the schema carries the parameter burden. The description restates the inputs at a high level (home size, system type, efficiency tier) but adds no format, unit, or default guidance beyond the schema, which is the baseline-3 case.

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+resource: it computes HVAC replacement/installation/repair cost. The domain term 'HVAC' cleanly separates it from its siblings (electrical, plumbing, roofing, solar, water-heater calculators) without the agent needing to open any 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?

The opening clause gives an explicit trigger condition: 'Use when a user asks what HVAC replacement, installation, or repair will cost.' That is clear routing guidance, but it names no exclusions and no alternative tool (e.g. what to use for a repair-only quote vs a full install), so it falls short of a 5.

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