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

Annotations already declare readOnly/idempotent/non-destructive and closed-world, so the safety profile is covered. The description adds real behavioral context beyond that: the ~120-station scope, the comparison baseline (same week's median since 2001), and the inclusion of prior-year same-week values and series extremes.

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-loads the core output (weekly average flow, comparator, scope) before the parameter-behavior clause. It is dense but every clause carries information; only mild trimming would be possible.

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?

For a read-only, two-parameter retrieval tool with no output schema, the description is nearly complete: it conveys the data source, units, comparison baseline, station coverage, and how parameters shape the response. A note on return granularity or units for the extremes would close the remaining 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 description coverage is 100%, so the schema already documents `cuenca` and `nombre`, including example formats. The description reinforces how each parameter changes the result (station vs. river, single basin vs. national summary) but adds little syntax or format detail beyond the schema, warranting the baseline 3.

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 resource and metric: weekly average flow (m³/s) of Spanish rivers at ~120 MITECO gauging stations, benchmarked against the seasonal median since 2001. The river-flow domain is clearly distinct from the reservoir-oriented siblings (estado_embalse, historico_embalse), so an agent can route correctly.

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?

Explains the two calling modes concretely: with `nombre` you get a station or all stations of a river; without it you get a Spain-level or basin-level summary highlighting the driest and highest rivers. It gives clear context but no explicit exclusions or named alternatives among siblings.

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