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

Annotations already establish this is a safe read-only, closed-world operation. The description adds real behavioral value beyond that: it discloses both compliance frameworks reported (WCAG ratios with AA/AAA thresholds split for normal vs large text, APCA Lc value and allowed usage level) and that a hue-preserving passing text color is suggested.

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 tight sentences, front-loaded with the primary action and framework coverage before the secondary suggestion behavior. Every clause carries information and nothing is padded.

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?

There is no output schema, so the description carries the return-value burden and does so well by enumerating ratios, AA/AAA levels, APCA Lc, and the suggested color. Only the accepted color input formats are unspecified, which leaves a small gap.

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%, so both parameters (text/foreground color, background color) are already documented in the schema. The description adds no accepted color syntax or format detail beyond that, so the baseline 3 applies.

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 (check) and resource (text contrast against a background) and names the two standards evaluated, WCAG 2 ratio/AA/AAA plus APCA Lc and usage level. It is less clear how it differs from the sibling fix_contrast, since it also advertises suggesting a passing text color.

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?

Usage is only implied by the metrics named – an agent can infer this is the tool for evaluating whether a foreground/background pair passes WCAG or APCA. No explicit when-to-use, no prerequisites, and no routing against siblings like fix_contrast, check_gamut, or compare_colors.

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