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

Annotations already declare read-only, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds genuinely new behavioural detail: a 404 failure mode and its usual cause (no floor area on record), the UK-only scope, and that the call is free. It stops short of 5 by not covering rate limits or latency for a model-backed endpoint.

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 tight sentences, front-loaded with what the tool returns, followed by failure behaviour and then scope/identity. Every clause carries information an agent needs; nothing is padding.

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-parameter tool with an output schema and full annotation coverage, the description covers purpose, failure mode, scope and the UPRN acquisition path. Nothing an agent needs in order 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% and the single parameter has no description, so the description must carry the load — and it does: it states the key is a UPRN, not an address, and explains how to obtain one via address_autocomplete/address_resolve. It never restates the integer type or required-ness, which is minor.

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 verb+resource ('Automated value estimate for a property') and even the return shape ('a point value plus a range'), so the agent knows what it gets back. It does not explicitly differentiate itself from close siblings such as valuation_full, valuation_comparables or equity_estimate, so it stops short of a 5.

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 real usage context: UK only, free, and keyed on a UPRN rather than an address, plus an explicit two-step path ('call address_autocomplete ... then address_resolve'). It never says when NOT to use it in favour of valuation_full or valuation_comparables, so it is clear context without exclusions.

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