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

Annotations already cover readOnly, idempotent, openWorld and non-destructive, so the bar is low, and the description adds genuinely useful context beyond them: the maximum 4-week history window and the monetization model (free within the daily allowance, then $0.003 USDC per call via x402). It does not describe pagination or truncation behavior when the result set exceeds _limit.

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 tight sentences, zero filler, with the resource and lookback window front-loaded and the cost note 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?

An output schema exists, so return values need not be explained, and the description covers the resource, the time window, and cost. The remaining gap is result-set handling (pagination/truncation at _limit) for what is a time-series history endpoint.

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. The description adds one real constraint not present in the schema – that `since` cannot go further back than 4 weeks – but says nothing about `_limit` behavior or station reference format beyond what the schema already documents.

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 ('Readings from a station') and scopes it with the since date-time and a 4-week lookback, which distinguishes it from uk-flood__station-latest and uk-flood__station. It stops short of naming those siblings explicitly, so an agent must infer the boundary between this and the latest-reading tool.

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 4-week lookback constraint and the pricing note imply when this tool is appropriate (historical series rather than current conditions), but there is no explicit when-to-use vs when-not, and no alternative sibling is named. Usage is inferable but not stated.

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