Contrast checker

Check the WCAG contrast ratio between a foreground color and a background color.

The tool calculates relative luminance for both hex colors, reports the contrast ratio, and marks whether the pair passes AA and AAA thresholds for normal and large text.

Thresholds

• AA normal text: 4.5:1
• AA large text: 3:1
• AAA normal text: 7:1
• AAA large text: 4.5:1

This is a browser-only calculation for design checks and accessibility reviews.

When to use it

Pick text and background colors during UI design, verify button labels on tinted headers, and document contrast decisions before hand-off to engineering. Invalid hex values return a clear error instead of a misleading ratio.

Limitations

Processing runs in your browser session; very large inputs may be slow or memory-heavy. Edge cases, locale-specific rules, and third-party API semantics may differ—verify critical results independently before relying on them in production or legal contexts.

Example

Black #000000 on white #ffffff yields contrast ratio 21:1.

This skill is available over A2A JSON-RPC and REST. When you already know the skill id and export, call execute directly—no discovery step required.

REST example

curl -sS -X POST https://toolplaza.app/api/helpers/execute \
  -H 'Content-Type: application/json' \
  -d '{"skillId":"colors__contrast-checker","export":"calculateContrastRatio","args":["#000000","#ffffff"]}'

A2A JSON-RPC example

Send POST https://toolplaza.app/api/a2a with:

{
  "jsonrpc": "2.0",
  "id": "1",
  "method": "message/send",
  "params": {
    "message": {
      "messageId": "uuid",
      "role": "user",
      "parts": [
        {
          "kind": "text",
          "text": "ignored"
        }
      ]
    },
    "metadata": {
      "toolplaza": {
        "skillId": "colors__contrast-checker",
        "export": "calculateContrastRatio",
        "args": [
          "#000000",
          "#ffffff"
        ]
      }
    }
  }
}

Full Agent API guide · Skill schema