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

With no annotations provided, the description carries the burden of behavioral disclosure. It reveals that results are 'ranked cleanest first' and provides label thresholds for interpreting carbon intensity levels. This adds meaningful behavior beyond the schema. It does not cover error handling or output format, but for a simple comparison tool, the disclosure is strong.

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 three sentences long, front-loaded with the core purpose, and every sentence adds value: the action, the use case, and the label definitions. There is no redundant or filler content.

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 tool with one simple parameter and no output schema, the description adequately covers the purpose, usage context, and even provides label ranges. It does not specify the exact return format (e.g., a list of zone-intensity pairs), but this is minor given the tool's simplicity. The description is sufficiently complete for an agent to invoke it correctly.

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 the 'zones' parameter as a comma-separated string with a max of 10. The description adds context that multiple zones are compared and orders results by cleanliness, but it does not introduce new parameter-level details beyond what the schema provides. This aligns with the baseline of 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?

The description clearly states the tool's function: 'Compare carbon intensity (gCO2/kWh) across multiple zones in one call, ranked cleanest first.' It specifies the resource (carbon intensity), the scope (multiple zones), and the key behavior (ranking). This distinguishes it from sibling tools like compare_green and compare_prices, which target 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 gives explicit use cases: 'Use when the user asks which grid is cleanest, or wants to find the lowest-carbon location to run a workload.' This tells the agent when to select this tool. However, it does not mention when not to use it or name alternatives (e.g., get_carbon_intensity for a single zone), so it falls short of a 5.

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