HueCheck Palette Lab

Check WCAG colour contrast, test whole palettes, and generate accessible 50-950 colour scales.

HueCheck Palette Lab is a WCAG color contrast checker and accessible color palette generator for designers, front-end developers and accessibility reviewers. It computes the exact WCAG 2.x contrast ratio for text and UI colours (hex, rgb, hsl, oklch, CSS names, and 8-digit hex with alpha), shows AA and AAA results for normal text, large text and UI components, suggests the nearest passing colours in OKLCH, tests every pair in a palette, and builds 50-950 tonal scales with CSS variables and a Tailwind config.

What it does

Exact WCAG 2.x contrast ratio, truncated to 2 decimals so a failing ratio is never shown as passing (4.499 fails AA)
AA and AAA for normal text, large text (24px, or 18.66px bold) and 3:1 for UI components and graphics
Nearest passing colours for AA and AAA, darker and lighter, changing only OKLCH lightness
Hex (with or without #), 8-digit hex with alpha, rgb(), hsl(), hwb(), lab(), lch(), oklab(), oklch(), color(display-p3 / srgb) and all 148 CSS colour names
Palette matrix: every pair of 2-12 colours, plus a recommended text colour for each background
50-950 OKLCH tonal scale with documented AA/AAA steps, CSS custom properties and a Tailwind config download
APCA Lc (WCAG 3 draft) shown as secondary, informational information

Try asking ChatGPT

“Check if white text on #F59E0B passes WCAG AA for body text”

“Check every pair in this palette: #1E6FD9, #F59E0B, #FFFFFF, #111827, #F3F4F6”

“Generate an accessible 50-950 color scale from #1E6FD9 with CSS variables and a Tailwind config”

Limitations

Checks colour values only: it cannot read colours from images, screenshots, PDFs or live web pages
WCAG 2.x contrast is a numeric test; it does not judge colour-blindness simulations, font weight rendering, or overall accessibility conformance
APCA values come from a draft method and are informational only
Translucent colours are composited in sRGB over the given background (or over white for palettes)

Connect

Install HueCheck Palette Lab from the ChatGPT plugin directory. Developers can connect the MCP endpoint directly: https://contrast-checker.zovo.one/mcp