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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so the safety profile is covered. The description adds genuinely new behavioral context: results are nearest-first, default radius 25 km, and the cost model (free within daily allowance, then $0.002 USDC per call via x402), which is material to invocation decisions.

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?

Two sentences, both earning their place: the first carries purpose, scope and defaults; the second carries the pricing model. Front-loaded with the core purpose and 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?

With an output schema present, return values need not be explained, and the description does note classification and pollution risk plus nearest-first ordering. Pricing, defaults and coverage are all present; only explicit sibling routing and parameter-format nuances are missing for a tool that is otherwise well-specified.

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 are already documented. The description restates the default radius, matching the schema, and adds no syntax or format detail beyond it (e.g. lat/lng string format or limit interaction with radius). Baseline 3 when the schema does the heavy lifting.

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 ('Designated bathing waters ... within a radius of a UK postcode or point'), plus scope, default radius, ordering, and returned fields. It is clearly a spatial-proximity query, which implicitly separates it from bathing-water__search and __site, but it never names or contrasts those siblings explicitly.

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?

Usage is implied by the spatial/radius framing and the postcode-or-lat/lng hint, but there is no explicit when-to-use guidance, no statement of when to prefer bathing-water__search or __site, and no mention of prerequisites. Adequate but with clear gaps.

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