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

Beyond the readOnlyHint annotation, it adds crucial behavioral semantics: null means no certificates lodged, whereas an error means the service is unreachable and should never be treated as evidence of absence. This error-vs-null distinction is a non-obvious defensive detail that prevents misinterpretation.

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?

The description is front-loaded with the primary purpose, then logically proceeds through address-dependent behavior, limitations, and null/error semantics. Each sentence carries necessary information with no redundancy or filler, making it efficient despite its length.

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?

Given the two-parameter schema, the presence of an output schema, and the readOnlyHint annotation, the description covers all behavioral aspects an agent needs: scope, conditional output, limitations, and error handling. Nothing essential for correct use is omitted.

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?

With 0% schema description coverage, the description compensates fully by explaining the effect of the address parameter: supplying it returns the matched certificate; omitting it returns record count and rating distribution. This workload-dependent behavior is essential for correct invocation and not deducible from the bare schema.

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 states a specific verb and resource: 'Energy Performance Certificate data for a UK property or postcode area.' It clearly distinguishes two modes (with and without address) and what each returns. It also explicitly lists unavailable aggregations, making its scope unmistakable even without naming a sibling.

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?

It gives clear context about when to use this tool (for a specific property or postcode summary) and what it does not provide (property-type breakdown, floor-area statistics), implying that a different tool would be needed for those. However, it does not explicitly name an alternative sibling tool, so the guidance stops short of a direct when-not.

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