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

Annotations already declare readOnly, idempotent, closed-world, and non-destructive, so the safety profile is covered. With no output schema, the description usefully enumerates what is actually returned (figures, boundaries, sources, limitations, citation line, divergence reasons), adding real value; it does not mention auth or freshness, but those are minor for a static read-only reference tool.

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 with zero waste: the first front-loads the full return payload, the second states the use case. Every clause earns its place, including the concrete 0.3–50 mL range that signals the tool's scope.

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 zero-parameter, read-only reference tool with no output schema, the description compensates by fully enumerating the return contents and the reason the tool exists. Nothing an agent needs in order to select and call it correctly 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?

The tool takes zero parameters, so there is nothing for the description to disambiguate. The baseline for a no-param tool applies, and the description correctly adds no spurious parameter discussion.

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 verb ('Return') and a well-defined resource: per-prompt energy/water figures, accounting boundaries, sources, limitations, citation line, and the ~100x divergence explanation. It is clearly distinguishable from the estimation siblings (compare/estimate) because this one retrieves methodology rather than computing a footprint.

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?

'Use it to explain or check a published AI water or energy figure' gives a concrete use context that separates it from the estimate_* and compare_* siblings. It stops short of explicitly naming an alternative tool or stating when NOT to use it, so it lands just below the top band.

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