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 genuine behavioral context beyond that: it discloses the tolerant name matching ('con o sin embalse de/pantano de/pantà de y sin tildes') and that the result includes a link to the embals.es record, neither of which is in the 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?

Two sentences: the first front-loads the resource and the returned fields, the second handles input tolerance. No filler, and the most decision-relevant content (what it returns) leads. Slightly dense but well organized.

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?

With no output schema, the description usefully enumerates the returned fields and the data date, and both input parameters are documented. It stops short of covering ambiguity/error behavior when a name matches multiple reservoirs or none, which would be the remaining gap for a lookup tool.

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. The description earns above baseline by documenting the accepted input forms for 'nombre' (optional prefixes, accent-insensitive, with examples) that the schema's minimal example does not cover; 'provincia' is left to the schema text.

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 gives a concrete resource ('un embalse de España') and enumerates exactly what is returned: fill percentage, stored water and capacity in hm³, weekly variation and data date. The phrase 'Nivel actual' implicitly distinguishes it from historico_embalse, but 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?

Usage is only implied: 'Nivel actual' signals a current-snapshot tool rather than the historical or search siblings, and 'provincia... solo para desambiguar' hints when the second parameter matters. There is no explicit when-to-use, when-not-to-use, or named alternative, so an agent must infer routing from the sibling names.

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