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

Annotations declare this is a read-only, idempotent, non-destructive, closed-world computation, so the safety profile is already covered. The description adds that the scoring uses a real WCAG contrast ratio, which is useful behavioral context, but says nothing about output shape, scoring scale, or limits. With annotations carrying the main burden, a 3 is appropriate.

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 first sentence is well front-loaded, but the second sentence is pure marketing ('See the full version at ...'), consuming roughly a third of the description without helping the agent decide whether or how to call the tool. Removing it would strictly improve the definition.

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 simple 4-param computation with a fully documented schema and read-only annotations, the description is minimally sufficient. Without an output schema, one line about what the score represents (e.g., range, pass/fail thresholds) would materially help the agent interpret results, and that 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 coverage is 100% with enum descriptions for size and placement and hex examples for the two color params, so the description doesn't need to restate them. It adds only that contrast ratio is computed from the hex colors, which is mildly informative but not beyond the schema. Baseline 3 is correct.

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 (score) and resource (CTA button visibility), and enumerates the inputs it uses: WCAG contrast ratio, size, and placement. Clear enough to distinguish from most siblings, though it doesn't explicitly contrast with typography_legibility_grader or above_the_fold_messaging_clarity_grader despite their adjacency.

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 usage (evaluating a CTA button's visual prominence) but gives no explicit when-to-use vs. when-not-to-use guidance and no named alternatives. In a field of 100+ sibling tools, that leaves routing to inference.

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