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

Annotations already declare read-only, idempotent, non-destructive, and closed-world behavior, so the safety profile is covered. The description adds real value beyond that: the official data provenance (MITECO), the since-1988 temporal span, and a breakdown of what the historical series contains. It omits return format/pagination, keeping it below 5.

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, zero filler: the first front-loads what the tool returns, the second front-loads the questions it answers. Every clause earns its place.

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 describes the returned series, data source, and temporal coverage, and all parameters are documented in the schema. Disambiguation guidance for 'provincia' is left to the schema text, so it is strong but not exhaustive.

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, and the description adds little syntax or format detail. It only loosely implies the years-back window via 'el nivel en la misma semana de cada año anterior', without tying that to the 'anos' parameter explicitly, so the baseline 3 is appropriate.

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 (weekly evolution of a reservoir) and its exact content: recent weeks, same-week values for each prior year, and period max/min, sourced from MITECO since 1988. This scope is instantly distinguishable from siblings like estado_embalse (current state) or buscar_embalses (search) without opening any schema.

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?

Provides explicit use-case framing via the questions it answers ('is it fuller than last year?', 'when was it this low?'), which tells the agent when this tool is the right pick. It does not, however, name alternatives or state when NOT to use it, so it stops short of full routing guidance.

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