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

Annotations already declare readOnlyHint=true and openWorldHint=false, so safety is covered. The description adds real value by signaling 'pure computation, free' — telling the agent there are no cost, auth, or network side effects and that the result is deterministic. It doesn't detail the return shape, but the flags hint at it.

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?

A single tight sentence with the core operation front-loaded and no filler. Every clause earns its place.

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 pure two-param computation with full schema coverage and annotations, the definition is nearly complete. It even describes part of the return ('AA/AAA pass flags'); only the exact response shape is unspecified, which is minor given no output schema.

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 100% with both parameters documented (including hex examples), so the schema carries parameter meaning. The description adds nothing beyond it, which fits the baseline 3 for full-coverage schemas.

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 computation ('WCAG contrast ratio between two hex colors') plus the output detail (AA/AAA pass flags). This distinguishes it clearly from sibling bursia_color_convert, which converts between color formats rather than evaluating accessibility.

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 phrase 'Pure computation, free' gives implicit context (cheap, deterministic, safe to call) but the description never says when to reach for this versus bursia_color_convert or other color tools, and offers no explicit exclusions.

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