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

Annotations already declare read-only, idempotent, closed-world, non-destructive, and the description is consistent with all of them while adding behaviour the annotations cannot express: multi-outcode towns return a list of options rather than data, and uncovered areas return the list of covered ones instead of failing. That disambiguation-then-retry behaviour is exactly the operational context an agent needs.

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-loaded with the resource and payload, then constraints, then the input contract, then the 'sold prices not valuations' caveat — a sensible ordering with no filler sentences. Slightly dense in the mid-section where coverage and multi-outcode handling interleave, but nothing is redundant.

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?

A single-parameter read-only aggregate with an output schema, and the description still covers the three things that schema and annotations cannot: what the numbers mean, the input ambiguity case, and the uncovered-area fallback. Nothing an agent needs to call this correctly is left to inference.

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% for the single 'area' parameter, so the baseline is 3; the description earns above that by spelling out the accepted forms (outcode, full postcode, or single-outcode town) and by explaining the consequence of passing an ambiguous town name. It adds the 'why' behind the parameter shape rather than restating the type.

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?

Opens with a specific verb-and-resource statement (sold-price figures for a UK postcode area from HM Land Registry) and enumerates exactly which statistics come back: median/quartile prices, breakdowns by property type, yearly medians, sector medians, and energy-rating counts. What's missing for a 5 is differentiation from the sibling 'nearby_sold', which an agent could easily confuse with this area-level aggregate.

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 concrete use-case phrasings ('what do flats sell for in CT20?', 'how have prices changed in Canterbury CT1?') and clear preconditions on the input — outcode, full postcode, or single-outcode town, with Folkestone given as the multi-outcode failure case. It also scopes what the tool is not (sold prices, not asking prices or valuations). It stops short of naming an alternative tool for out-of-scope questions.

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