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

Annotations already declare readOnlyHint and openWorldHint, so the safety profile is covered. The description adds genuinely useful non-schema context: a per-call cost of $0.05 paid in USDC on Base via x402, plus the explicit statement that no address-level records are returned.

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?

Three short sentences, front-loaded with the core purpose, then the geographic limitation, then the cost. Every sentence adds information; the only nit is that the cost caveat would read better after the scope caveat rather than as a trailing sentence.

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?

There is no output schema, but the description says enough about the shape of the result (share of ratings A-G per postcode district) for an agent to interpret the return value. Still, for a five-parameter tool with only 20% schema coverage, the missing explanation of the time window and the minimum-certificate filter leaves gaps that matter for correct invocation.

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 only 20%, so the description must carry weight: it maps to 'one council' (required), 'per postcode district' (one groupBy option), and 'homes or commercial buildings' (buildingType domestic/non_domestic). However, it never explains the 'months' lookback or 'minCertificates' threshold, nor the constituency/council groupBy options, leaving real gaps.

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 concrete verb+resource: EPC statistics for one council in England or Wales, broken down by rating band A-G and geography. The scope qualifier 'Area-level only, no addresses' helps distinguish it from a sibling like property_area, but no sibling is named explicitly.

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 'area-level only, no addresses' constraint, which signals when not to use it, and by naming the geographic unit as a council. It never states alternatives, prerequisites, or when to pick a different geographic breakdown tool.

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