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

Beyond the annotations (readOnly, openWorld, idempotent, non-destructive), the description discloses the data source (environment.data.gov.uk/hydrology), the licensing (UK Open Government Licence v3.0), and that no authentication is required. It also highlights the uppercase TEMPERATURE quirk and confirms it's an upstream data behavior. This adds meaningful context not captured by annotations.

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?

The description is comprehensive but not excessively long. It front-loads the core purpose, then provides examples, optional filter details, output fields, usage with other tools, and licensing. Each sentence contributes value, though it could be slightly more concise by omitting redundancy with the schema. It's well-organized and readable.

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?

Given the presence of an output schema, the description adequately covers the essential context: how to obtain the station_id, what the tool returns (measure_id, period, value type, unit), and how to use the result with subsequent tools. It also includes licensing and auth info. It doesn't mention pagination or error handling, but for a listing tool of this scope, the information is sufficient.

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?

The schema already provides full descriptions for both parameters, including the enum values and the uppercase note for TEMPERATURE, and the station_id example. The description adds little beyond what the schema states; it repeats the filter values and the station_id origin. Since schema coverage is 100%, the baseline is 3, and the description doesn't elevate it.

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?

The description states a specific verb (List) and resource (data series/measures at an EA hydrology station), with concrete examples (15-minute flow, daily mean/min/max level, daily rainfall). It clearly differentiates from sibling tools like ea-hydrology.readings.latest by explaining that this returns measures, not readings, and that the result should be used with those tools. The purpose is unambiguous and distinct.

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 description explicitly instructs to use the station_id from ea-hydrology.station_search, establishing a prerequisite and sequential workflow. It also directs the agent to use the returned measure_id with ea-hydrology.readings.latest or ea-hydrology.readings.range, clarifying how this tool fits into a larger pipeline. However, it doesn't explicitly state when NOT to use this tool (e.g., if you already have a measure_id), but the guidance is clear enough for correct invocation.

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