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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), and the description adds materially more: a cost of 15 credits, the UK-only constraint, the conditional emission rule for `price_trajectory` (only with two-plus priced snapshots), and the semantic that an empty result is a valid answer rather than an error. None of this is recoverable from structured fields.

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 its contents, then constraints, then the routing instruction. Every sentence carries distinct information (scope, cost, conditional field, empty-result semantics, acquisition path) with no filler.

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 single-parameter lookup with an output schema present, the description supplies everything an agent needs: what the resource is, the geographic limit, the credit cost, the key format and how to derive it, and how to interpret a null result.

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 in the schema, so the description must carry the load — and it does, explaining that the key is a UPRN rather than an address and how to obtain one via address_autocomplete/address_resolve. It stops short of describing the UPRN's format or integer type, so it is not fully exhaustive.

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+resource ('Every marketing snapshot for a property') and then enumerates exactly what is returned — asking price over time, reductions, days listed, status changes, agent, image count, floor plan. This is clearly distinguishable from siblings like property_history, property_media or listing_market_series.

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 explicit prerequisites and a workflow: 'Keyed on a UPRN, not an address: call address_autocomplete (free) to narrow, then address_resolve to get one.' It also pre-empts a false-negative by stating no listing is a real answer, and scopes the tool geographically (UK only).

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