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

Adds value beyond the readOnly/idempotent/openWorld annotations: upstream source (Environment Agency flood-monitoring API), that the series is downsampled rather than raw, that it is not a forecast, and a 1-credit cost. With annotations already covering the safety profile, this is solid but not rich - no mention of rate limits, error behavior for bad station IDs, or update cadence.

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?

Front-loaded with what the tool returns before the framing sentence and caveats. Mildly dense with parentheticals, but every clause carries information (defaults, window limit, non-forecast caveat, cost).

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?

No output schema exists, and the description compensates by enumerating the returned summary fields (min, max, change since start, rising/falling/steady) plus the thinning caveat. A user could call it correctly; only failure modes and station-ID discovery are unaddressed.

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 three parameters are already documented in the schema. The description restates the 'since' default and 7-day bound but adds no format examples or guidance on choosing 'points' beyond what the schema says. 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?

States a concrete verb and resource: river level readings at one gauge over a time window, with summary statistics. The 'history' scope plus the 7-day limit implicitly separates it from river_level_now and river_level_record, though no sibling is named 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?

Gives a real use case ('has the river peaked yet' for flood watchers and anglers) and constraints (up to 7 days back, not a forecast). It never names an alternative tool to use instead, so the when-not guidance is only implied by the time-window framing.

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