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

Annotations already declare readOnly, idempotent, non-destructive and open-world, so safety is covered. The description adds genuinely useful behavior: the 'nearest first' ordering, the default and capped radius, and the pricing model (free daily allowance, then $0.002 USDC via x402). That pricing/ordering context is not available in the 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?

Two sentences, zero waste, with the core operation and scope front-loaded and the pricing caveat trailing where it belongs.

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 described, and the annotations carry the safety profile. The description fills in scope, ordering, radius bounds and pricing, leaving only sibling disambiguation as a gap.

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 description coverage is 100%, so the baseline is 3, but the description adds the max radius cap (25 km) that the schema does not state, reinforces the 10 km default, and conveys result ordering. It still does not clarify the lat/lng vs. postcode fallback relationship beyond what the schema implies.

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+resource ('stations within a radius of a postcode or point') and enumerates the data types covered (level, flow, rainfall, groundwater), so the operation is unambiguous. It does not, however, differentiate itself from close siblings like uk-flood__stations-near or uk-rivers__rainfall-near, so an agent cannot tell which near-search tool to pick from the text alone.

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?

The 'near a point' framing implies the geographic-proximity use case, and the default/max radius hints at scope. But there is no explicit when-to-use vs. when-not guidance and no alternative named, which matters given the several near/station siblings in this family.

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