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

Annotations already declare readOnlyHint=true and openWorldHint=false, and the description adds genuinely useful behavioral context: the fix preserves hue and character by mutating only OKLCH lightness, which tells the agent what the transformation will and won't do. It does not describe the shape of the returned result, but with a safe read-only profile the bar is lower.

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, front-loaded with the core mechanism before the target enumeration. The target list is long but each entry earns its place by decoding the enum; no filler sentences.

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 4-parameter, read-only, no-output-schema tool, the description covers the operation, the adjustable inputs, and the full target vocabulary. The only mild gap is that it doesn't state what the response contains (presumably the adjusted color pair), but no output schema exists to make that omission costly.

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 coverage is only 50%, and the description compensates well by spelling out what each target enum value actually means numerically (aa = 4.5:1, aaa = 7:1, apca-body = Lc 75, etc.) and by explaining that 'adjust' selects text vs background. The two color parameters are already documented in the 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?

States a specific verb (find/fix) plus the exact mechanism: the closest color reaching a contrast target, achieved by changing only OKLCH lightness. This is sharply distinguishable from siblings like check_contrast (measures) or audit_palette (bulk audit), which an agent can infer without opening schemas.

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 implies when to use it (a color pair fails a contrast requirement and needs remediation) and clarifies that either text or background may be adjusted. However, it never explicitly contrasts itself with check_contrast or audit_palette, nor states when not to use it.

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