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

With no annotations, the description carries the full burden and does: it declares the tool 'Read-only and deterministic ... stores nothing, so it is safe to call repeatedly with no side effects.' It also discloses non-obvious behavior such as paint's per-RGB-channel dominance (yellow + css:blue comes out black) and the brand-name-over-CSS-name collision rule.

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 core purpose is front-loaded and every section is functional, but the description is long and the #00b0a0/#9cc1a5 numeric anecdote plus the channel-dominance example push well past what an agent needs to select and call the tool, somewhat diluting signal.

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 3-parameter tool with an output schema, the description covers inputs, all mode semantics, default selection, collision rules, edge cases, side-effect profile, and sibling disambiguation. The output schema covers the return shape ('Returns hex and rgb' is also noted), so nothing material 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 description coverage is 0%, so the description must fully explain the three parameters — and it does. It enumerates the accepted color formats (hex, CSS name, RNV brand name, saved-palette reference with swatch index syntax), explains weights as optional integers defaulting to equal, and spells out the semantics of every mode value including which is the default (lab).

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 first sentence states a specific verb and resource with scope: 'Blend up to 12 colors into one.' It further distinguishes itself by naming the exact sibling alternatives (convert_color for format conversion, color_difference for distance measurement), so an agent can route correctly without opening any schema.

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?

It gives explicit when-to-use guidance for each mode: 'paint when BLENDING brand colors into a new one, and lab when SAMPLING between them,' with a concrete failure anecdote (#00b0a0 vs #9cc1a5). It closes with an explicit routing block naming when to use convert_color and color_difference instead.

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