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

With no annotations provided, the description carries full responsibility for behavioral disclosure. It states 'Read-only and deterministic, with no side effects,' which covers the safety profile, and explains the return value ('Returns the value and a plain-language interpretation'). This meets the bar for transparency.

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 well-structured: purpose first, then parameter formats, method selection, return value, safety note, and usage guidance. Every sentence adds value, and the length is appropriate for the tool's complexity.

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?

Given the output schema exists, the description needn't detail return structure, but it still does. It covers input formats, method semantics, output interpretation, safety, and comparative guidance. This is a complete, self-contained tool description.

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?

Despite 0% schema description coverage, the description fully explains all three parameters: color1/color2 accept hex, CSS name, RNV brand name, or saved-palette reference, and method is 'ciede2000' (default) or 'cie76'. This compensates completely for the sparse schema.

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 opens with a specific verb and resource: 'Perceptual difference (Delta-E) between two colors.' It clearly distinguishes the tool from siblings by naming contrast_check, which serves a different purpose (legibility rather than raw difference). This is unambiguous and identifiable.

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 states when to use each method ('Use ciede2000 for accuracy and pick cie76 only to match a legacy system') and provides a direct alternative ('to test whether text is legible on a background ... use contrast_check instead'). This gives the agent clear decision criteria.

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