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

Annotations only cover the safety profile (readOnly, idempotent, non-destructive); the description adds substantial context beyond them: result-count caps, the meaning of a null `retrofit_gap` versus zero, interpretation caveats (habitable rooms are not bedrooms, changes don't prove works), UK-only scope, and that the tool is free and keyed on UPRN.

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?

Front-loads the return shape before the caveats, and every sentence carries interpretive value. It is dense and slightly long for a single-parameter tool, but there is little genuine filler.

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 one-param read tool with an output schema and full safety annotations, the description covers the remaining burden: how to supply the key, what a null gap means, how to read the results, and the geographic/scope limits. Nothing needed to call 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% for the single `uprn` parameter, but the description compensates by explaining that the key is a UPRN rather than an address and narrating exactly how to obtain one via `address_autocomplete`/`address_resolve`.

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 (Energy Performance Certificates) for a specific key (a property/UPRN) and the exact return shape ('newest first: up to five mart certificates and up to five raw certificates'). This clearly separates it from siblings like energy_profile, property_energy_retrofit, or property_summary.

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 an explicit prerequisite workflow — call `address_autocomplete` then `address_resolve` to obtain the UPRN — and clarifies that an empty result is a valid answer rather than a failure. It lacks explicit when-not guidance versus other energy/retrofit siblings, so it stops short of a 5.

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