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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false and openWorldHint=false, so the safety profile is covered. The description adds genuinely useful behavior beyond that: a 20-credit cost, UK-only coverage, and an explanation of why pitch/orientation/shading are absent. The only reason this is a 3 rather than higher: it doesn't cover the batch nature of the call, rate limits, or partial-failure behavior for a multi-UPRN request.

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 sentences, each carrying distinct information — contents, deliberate exclusion, coverage/cost, and keying/routing — with the most important constraint front-loaded. No filler or restatement of the name.

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 spends its budget on what an agent cannot get from structured fields — the deliberate absence of yield data, UK scope, credit cost, and UPRN acquisition path. Complete for a one-parameter read tool with annotations covering safety.

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% and the single parameter is an opaque integer array named 'uprns'. The description compensates well by stating it is keyed on a UPRN (not an address) and where to get one, which is the critical semantic the schema omits. It does not say whether multiple UPRNs are meaningfully supported in one call or what the integer format expects, leaving a small gap.

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 names a specific resource (roof characteristics for solar screening) and enumerates exactly what comes back: footprint area, roof shape and material, building height, existing panels. It also states a deliberate negative — no generation estimate — which prevents the agent from misreading it as a yield tool, cleanly separating it from siblings like energy_profile or property_energy_retrofit.

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?

Explicit prerequisites and routing: UK only, costs 20 credits, keyed on UPRN and not address, with the exact two-step path (address_autocomplete then address_resolve) to obtain one. It also tells the agent how to report results ('report the usable roof area as a screening figure and say what it excludes'), which is actionable guidance rather than inference.

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