Check a colour pair against WCAG

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

Annotations already indicate read-only (readOnlyHint=true). The description adds behavioral detail beyond annotations: token resolution per theme and compositing translucent values over the page. This gives the agent important context about how inputs are processed without contradicting the annotations.

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 two sentences, front-loaded with the core function, and each sentence earns its place. No fluff or repetition of schema details.

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?

The tool is simple and low-complexity. The description mentions the output (ratio and pass/fail verdict) and the schema covers thresholds via enum descriptions. It is complete enough for an agent to understand the tool's behavior without an 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 coverage is 100% and each parameter has a meaningful description. The tool description adds minimal extra parameter semantics—only the note about compositing translucent values—which is somewhat beyond the schema but not substantial. Baseline 3 is appropriate.

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 clearly states a specific verb ('Check') and resource ('colour pair against WCAG'), and specifies WCAG 2.2 contrast ratio and pass/fail verdict. This distinguishes it from all sibling tools, none of which mention contrast or WCAG.

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 conveys clear usage context: it accepts hex values or token names and resolves tokens for the chosen theme. It does not explicitly state when not to use it, but the uniqueness among siblings and the specific focus on contrast make the intended use obvious.

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