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

Read-only and closed-world behavior are already covered by annotations, so the description's added value is the calculation logic and the set of computed outputs. It still does not describe the response shape or rounding behavior, but it meaningfully discloses how the calculation works.

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 description is front-loaded with the core purpose, then provides the formulas compactly. It is dense but every part earns its place for a calculation tool.

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?

All parameters are optional with schema defaults, and although there is no output schema, the description enumerates the expected outputs: required Btu/h, gas input, electric kW, and amps. This is sufficient for an agent to understand the tool's result.

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 the baseline would be 3, but the description adds relationships between parameters: temperature rise, heat output from gpm and rise, gas input from efficiency, and amps from kW and volts. This meaningfully supplements the per-field schema descriptions.

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: sizing a tankless water heater from peak flow and temperature rise. It also names the computed outputs, making it clearly distinct from siblings such as calc_pool_heater_size or calc_generator_size.

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 intended use is implied by the name and by 'Size a tankless water heater from your peak hot-water flow...', but there is no explicit when-to-use or when-not-to-use guidance. It does not mention alternatives or prerequisites beyond the formula context.

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