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

Annotations already declare readOnlyHint and openWorldHint, so the description adds real value on top: the data provenance (official OGL open data), the historic-vs-current data limitation, and precise billing terms ($0.002 USDC per successful call via x402, failures uncharged). Payment/auth behavior is exactly the kind of context annotations can't carry; only the return-shape is left to the output schema.

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 tight sentences, front-loaded with what the tool returns, then data provenance, then the critical listing-vs-sales distinction, then cost. No filler or repetition.

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?

With an output schema handling return values, full schema descriptions, and annotations covering safety, the description supplies the remaining essentials: provenance, the historic-data limitation, and billing. An agent has everything needed to decide and call correctly.

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%, with both `postcode` (example SE1 7PB) and `limit` (1–50) already documented in the schema. The description reinforces that results are for a single postcode but adds no format or range detail beyond what the schema provides, so 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 verb and resource ('Recorded UK residential sale prices and dates for one postcode') plus the exact data source (HM Land Registry Price Paid Data). The clause 'Historic sales only, not current listings' separates it from the listing-oriented siblings like realestate_zoopla or realestate_rightmove_property.

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?

Explicitly states the when-not condition ('Historic sales only, not current listings') and clarifies that Purplebricks has no public API, which explains the naming. It stops short of naming a concrete alternative tool for current listings, leaving the agent to infer one from the sibling set.

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