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

Annotations already cover the safety profile (read-only, idempotent, non-destructive, open-world), and the description adds genuinely new behavioral context: the free daily allowance and the $0.002 USDC x402 micropayment once exceeded. It stops short of explaining the geometry cap or what 'region' boundaries mean.

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 crisp, front-loaded sentences with no filler; the purpose leads and pricing follows. The middle sentence largely duplicates the schema's postcode/lat-lng description, a small redundancy.

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 present, return values need no explanation, and annotations plus the pricing note cover the operational context. The remaining gap is disambiguation from the sibling region tool and any note on how lat/lng vs postcode resolution behaves.

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%, so all five parameters including geometry and include_ended are already documented in the schema; the description only restates the postcode/lat-lng choice and adds no new syntax or format meaning. 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?

'The English region for a point' states the resource and the return, but the verb is implicit and there is no differentiation from the near-identically named sibling uk-geography__region, which an agent would have trouble choosing between.

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?

'By UK postcode or lat/lng' tells the agent which inputs are acceptable, which implies usage, but gives no when-to-use/when-not guidance and never names an alternative to disambiguate from uk-geography__region or the other uk-planning point lookups.

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