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

The annotations already declare readOnlyHint, openWorldHint=false, idempotentHint and destructiveHint=false, so restating "read-only, no network, no state, deterministic" is largely redundant. What the description genuinely adds beyond structured data are the operational limits — 64 KB JSON input, 1 s per call, 1 MB result — which are not encoded in any annotation or schema.

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?

Each block is tight and front-loaded: capability, then When / Not for, then side effects, then limits. The only cost is that the entire text is duplicated verbatim in Spanish and English, doubling length without adding information for a reader who parses both.

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 single-parameter, deterministic, read-only conversion with a fully documented schema, a declared output schema, and complete annotations, nothing an agent needs is missing — routing, semantics, limits and determinism are all covered.

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?

With one parameter at 100% schema coverage, the baseline is 3; the description goes slightly beyond by framing kelvin as a black-body light-source temperature and tying it to real-world reference values (2700 K warm white, 6500 K daylight), which helps an agent pick a sensible input rather than just a bounded number.

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?

"Approximates the sRGB color of a black-body light source at a temperature from 1,000 K to 40,000 K" states a concrete verb, a precise resource, and an explicit domain range, plus the implementation fit (Tanner Helland) and concrete examples (2700 K warm white, 6500 K daylight). It is instantly distinguishable from color-convert, color-mix and color-adjust.

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?

Contains explicit "When:" guidance (computing exact color values, contrast, palettes, accessibility checks) and an explicit "Not for:" that names the correct alternative sibling (color-adjust for OKLCH). Both the positive and negative routing conditions are stated rather than implied.

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