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

Annotations already declare readOnly, idempotent, non-destructive and open-world, so safety is covered. The description adds genuinely new behavioral context: this is a metered call charged against a Stratum API balance, with a test key available — information that affects whether and how often an agent invokes it. It stops short of saying what happens when no certificate exists for the postcode.

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?

A single front-loaded sentence: what it returns first, billing context second. No restatement of the name or title, no 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 2-parameter read tool with full schema coverage and an output-free annotations set, the description is nearly complete — it names the returned values and the cost model. The one meaningful gap is the no-EPC-found case, which no structured field covers.

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 100% and both parameters (postcode required, addressLine1 optional for disambiguation) are described in the schema itself. The description adds no parameter-level meaning, so the baseline 3 applies.

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 (the latest EPC for a property) and the two values returned (rating and MEES compliance), so an agent knows exactly what it fetches. It does not explicitly differentiate itself from the sibling postcode_report, which also takes a postcode, so the sibling boundary is left implicit.

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 only implied by the resource name — an agent infers 'call this when you need an EPC/MEES check for a UK property'. There is no when-not guidance (e.g. what to do if the property has no EPC) and no mention of the alternative postcode_report for broader property data.

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