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

Annotations already establish readOnly, idempotent, non-destructive behavior, so the description's job is to add computation context, which it does: it keeps NAHB and InterNACHI life guidance separate, applies EPA age guidance, uses the DOE repair comparison against user-supplied quotes, and returns historical vs. modeled references as distinct labels. It does not explain the response shape or how the labeled references are structured, which keeps it below 5.

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?

A single dense sentence that is front-loaded with the core purpose (estimate furnace age from serial or confirmed date) followed by side-effect details. Every clause carries information, though the sentence is long enough that it reads as a run-on rather than crisply sectioned text.

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 9-parameter, no-output-schema tool, the description covers the key inputs (serial format confirmation, maker-confirmed date override) and the nature of the output (separately labeled historical and modeled replacement references). It stops short of describing the return structure in any detail, which leaves a modest gap given there is no 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%, so parameter documentation is already handled by the schema. The description reinforces the confirmation requirements (format_confirmed, maker-confirmed century/date) and the separation of the two quote inputs, but adds no format or syntax detail beyond what the schema already provides; baseline 3 is appropriate.

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 (estimate) and resource (furnace manufacture age) and scopes it to enumerated serial formats (Lennox legacy, Rheem, Nordyne) plus a maker-confirmed date fallback. No sibling tool covers furnace age, and the input conditions are clear enough that an agent can distinguish it from generic calculators like calendar_age_difference.

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 description implies the required preconditions for use: a confirmed serial format or a maker-confirmed manufacture date, and other brands requiring dealer confirmation. It gives clear context for when the tool applies but does not explicitly state exclusions or when a different tool should be used instead.

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