io.github.ogSINGH/contrast-checker-mcp

contrast-checker-mcp

An MCP server that provides color contrast checking tools for AI assistants. Verify WCAG 2.1 accessibility compliance, compute contrast ratios with alpha transparency support, and get accessible color suggestions — all via the standard Model Context Protocol.

Contrast calculations match WebAIM's contrast checker — including alpha compositing, WCAG 0.03928 sRGB threshold, and truncated (not rounded) ratios.

Tools

check_contrast

Check the contrast ratio between two colors and evaluate WCAG 2.1 compliance.

Inputs:

• foreground — Foreground color (e.g. #333, rgb(0,0,0), rgba(0,0,0,0.5), navy)
• background — Background color (e.g. #fff, rgb(255,255,255), white)

Output: Contrast ratio, WCAG 2.1 pass/fail results (AA normal, AA large, AAA normal, AAA large), parsed color values. When the foreground has alpha, shows the effective composited color used for the calculation.

suggest_accessible_color

Suggest a replacement color that meets a WCAG contrast target, keeping the hue as close to the original as possible.

Inputs:

• foreground — Foreground color
• background — Background color
• target_level — "AA" or "AAA" (default: "AA")
• fix — "foreground" or "background" (default: "foreground")

Output: A suggested replacement color (in hex, rgb, hsl) that meets the target level, along with the new contrast ratio.

parse_color

Parse a color string and return it in multiple formats.

Inputs:

• color — Color to parse (e.g. #ff6600, rgb(255,102,0), tomato)

Output: The color in hex, rgb, and hsl formats.

Supported Color Formats

• Hex: #rgb, #rrggbb, #rgba, #rrggbbaa
• RGB: rgb(r, g, b), rgba(r, g, b, a)
• HSL: hsl(h, s%, l%), hsla(h, s%, l%, a)
• CSS named colors: red, cornflowerblue, rebeccapurple, etc.

Setup

Claude Desktop

Add to ~/Library/Application Support/Claude/claude_desktop_config.json (macOS) or %APPDATA%\Claude\claude_desktop_config.json (Windows):

{
  "mcpServers": {
    "contrast-checker": {
      "command": "npx",
      "args": ["-y", "contrast-checker-mcp"]
    }
  }
}

Claude Code

claude mcp add contrast-checker npx -y contrast-checker-mcp

Cursor / VS Code

Add to .cursor/mcp.json or .vscode/mcp.json:

{
  "servers": {
    "contrast-checker": {
      "command": "npx",
      "args": ["-y", "contrast-checker-mcp"]
    }
  }
}

From source

git clone https://github.com/ogSINGH/contrast-checker-mcp.git
cd contrast-checker-mcp
npm install
npm run build
node dist/index.js

Examples

Black on white — 21:1 ratio, all WCAG levels pass:

check_contrast({ foreground: "#000000", background: "#ffffff" })

Semi-transparent text — alpha composited onto background before checking:

check_contrast({ foreground: "rgba(0,0,0,0.5)", background: "#ffffff" })
→ effective color #808080, ratio 3.94:1

Fix a failing color pair:

suggest_accessible_color({
  foreground: "#777777",
  background: "#ffffff",
  target_level: "AA"
})
→ suggests #757575 (4.61:1)

License

Apache-2.0