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

Annotations already establish readOnly, idempotent, and non-destructive, so the safety profile is covered. The description adds genuinely useful non-schema context: the free daily allowance and the $0.002 USDC x402 charge after it. It stops short of saying what happens when a station has no measure of the requested type.

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 load-bearing, with the core behavior front-loaded ahead of the cost note. Slightly dense in the first sentence but no padding or restatement of the title.

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?

An output schema exists, so return values need not be explained. For a two-param read-only lookup the description covers purpose and cost adequately; only empty-result and unknown-station behavior are left unstated, which is a minor 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 coverage is 100% and the type param already enumerates 'level | flow | rainfall | groundwater', which the description merely restates. The phrase 'for each measure of a type' hints that results may be multiple per station, but no added syntax or format detail beyond the schema.

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: the latest reading per measure of a given type at a station. It is distinguishable from uk-rivers__readings in spirit (latest vs. historical) but never names or contrasts those siblings, so the agent must infer the boundary from naming 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?

No guidance on when to choose this over uk-rivers__readings, uk-rivers__station, or uk-flood__station-latest, and no prerequisites stated beyond the pricing note. The only conditional content concerns billing, not tool selection.

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