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

Annotations already cover the safety profile (readOnly, idempotent, closed-world), and the description adds genuinely non-structured facts: UK-only coverage and a 30-credit cost per call, plus the default band behavior and the ranking basis. These are exactly the constraints an agent needs before spending credits.

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?

Four short paragraphs, each earning its place: purpose first, then framing (targeting vs fact), then the key parameter/filter idiom, then hard constraints. No filler or restatement of the title.

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 shape need not be described; the description instead covers the decisions an agent must make — geographic eligibility, credit cost, filter defaults, and ID provenance. Nothing needed to invoke it correctly 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 coverage is 0%, so the description carries the burden and does well: area_id is tied to the marts area id from area_resolve, fuel is illustrated with the 'gas' fossil-heated cohort, and bands is explained as defaulting to E/F/G (clarifying the null default). Only `limit` is left undocumented, which keeps it below a 5.

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 resource (properties in an area), a specific ranking criterion (improvement headroom / potential efficiency), and explicitly contrasts itself with single-property tools: 'it returns a list to act on, not a fact about one property.' An agent can distinguish it from property_energy_retrofit and energy_profile without opening 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?

Gives clear operational guidance: default band set E/F/G, the fuel='gas' cohort pattern, and that area_id must come from area_resolve. It stops short of explicitly naming when to prefer a sibling (e.g. property_energy_retrofit for a single address), so it is clear context without full exclusion rules.

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