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

Annotations already declare readOnlyHint, openWorldHint=false, and destructiveHint=false, so the bar is lower; the description still adds real behavior: a neutral ordering rule, no paid placements, and a member-first-then-researched fallback with geographic coverage limits. The one notable gap is that it never describes the shape of what comes back, and no output schema exists to cover that.

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 core purpose is front-loaded correctly, but the anti-pay-to-play point is restated three times ('membership and listing are free,' 'optional paid tools do not affect ordering,' 'no paid placements'), which is redundant wording that does not earn its space.

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 simple two-parameter read tool, the description covers ordering, coverage limits, inclusion criteria, and a key limitation (cannot contact companies). Without an output schema, a short note on what each result contains would close the remaining gap.

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%, including the 'only if it applies' guidance on the job array, so the schema already carries parameter meaning. The description does not mention zip or job at all, leaving it at the baseline rather than adding anything.

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 first clause names a specific verb and resource with scope: 'Lists HRV and ERV installer companies for a US ZIP code.' That is clearly distinct from siblings like find_rebates and check_ventilation_unit, so an agent can route without opening a 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?

Usage is implied by the purpose statement plus the coverage caveat (Colorado Front Range and New England only), which helps an agent predict empty results. However, there is no explicit when-to-use framing and no named alternative among the siblings (e.g., when to prefer find_rebates or units_to_ask_about instead).

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