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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=true, so the description does not need to re-establish the safety profile. It adds real value beyond that: the upstream source is the EPA's official data, list results are ordered most-efficient-first, and heat pump answers carry the 25C/25D tax-credit expiry. It does not mention result caps or pagination, which keeps it off a 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?

Purpose and usage are front-loaded in the first two sentences, and the tax-credit caveat is genuinely non-obvious domain context worth keeping. The inline category enumeration partially duplicates the schema enum, which is mild redundancy but not harmful for scannability.

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?

An output schema exists, so return-value detail is correctly omitted, and the description covers both operating modes (certification lookup vs. ranked listing) plus domain scope and exclusions. For a 4-parameter read-only lookup with full schema coverage, nothing an agent needs to invoke it is missing.

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 enum for category and the note that most_efficient_only is unavailable for water heaters; the description mostly restates the category list and the efficiency ordering already encoded in the schema. Baseline 3 is correct because the schema does the parameter-level work.

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 and resource: check ENERGY STAR certification for a model, or list certified models, from EPA data. It enumerates the supported categories and explicitly disclaims two adjacent domains (prices, recalls), so an agent can distinguish it from compare_prices and check_recalls 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?

Gives explicit trigger conditions ("Use this when someone asks if a model is ENERGY STAR, which models are most efficient, or about energy-efficient appliance choices") and names the alternatives for the excluded cases (compare_prices, recalls). Nothing about when to select this tool is left to inference.

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