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

Annotations already establish read-only, idempotent, non-destructive behavior, and the description adds meaningful context: the data source URL, UK Open Government Licence, no-auth requirement, inclusive date bounds, and the reading fields returned. This goes beyond the structured hints without contradicting them.

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?

Three short sentences with the core operation first, followed by the required parameters and one sentence on source, licence, and auth. No filler, tautology, or unnecessary repetition of schema details.

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?

The description is largely complete: it names the upstream data source, licence, auth status, required parameters, and output fields, while the output schema covers return structure. The only gap is the inaccurate cross-reference to 'ea-hydrology.station_measures' instead of the actual sibling 'ea-hydrology.stations.measures,' which an agent may need to resolve.

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 the baseline is 3, but the description adds value by emphasizing that min_date and max_date are required, specifying YYYY-MM-DD and inclusive bounds, and explaining that measure_id comes from the companion measures tool. The only minor flaw is the slightly inconsistent reference to 'ea-hydrology.station_measures' rather than the exact sibling name.

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 opens with a specific verb and resource: 'Get a date-ranged time series of readings' for 'one EA hydrology data series,' and it names the returned fields (date, value, quality, completeness). This clearly distinguishes the range query from the sibling ea-hydrology.readings.latest and orients the agent toward the correct use case.

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?

It states the primary context: historical date-ranged readings for a single measure, and gives the prerequisite that measure_id comes from the stations/measures lookup. It does not explicitly name alternative tools or state when not to use this one, so it stops short of full exclusion guidance.

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