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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the agent knows this is a safe query. The description adds the exact fields returned (source breakdown, percentages) which is useful context, but doesn't go beyond annotations to discuss rate limits, caching, or response format. Since annotations cover safety, a 3 is appropriate—the description adds some value but not rich behavioral context.

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 a single, information-dense sentence plus an example call. The primary purpose is front-loaded, and every element earns its place—no fluff or repetition of schema details. The example reinforces the input pattern efficiently.

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?

There is no output schema, so the description must explain the return content, which it does (sources listed, percentages). It also fully covers input requirements (zone/lat+lon, API key). For a read-only, idempotent tool with annotations, nothing essential is missing.

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% (all four parameters have descriptions). The description reinforces key semantics: it explains the zone vs lat/lon alternation, gives example codes, and emphasizes that _apiKey is required. This adds value beyond the schema by clarifying the relationship between parameters and typical usage patterns.

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 action (get power generation mix) with a clear resource (a zone or lat/lon) and enumerates the output fields (breakdown by source plus fossil-free and renewable percentages). This clearly distinguishes it from sibling tools like carbon_intensity or carbon_forecast, which focus on different metrics.

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 says to pass a zone code or lat+lon and gives concrete examples (FR, US-CAL-CISO). It implies when to use it (when you need power mix rather than carbon metrics), but does not explicitly name alternatives or state when NOT to use it. This is clear enough for an agent, but could be slightly stronger with explicit routing to sibling tools.

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