WCAG Color Contrast Checker Online Free — Accessibility Contrast Ratio Tool

Overview: Verify color accessibility and WCAG AA/AAA compliance for text and UI elements.

Calculate color contrast ratios and evaluate accessibility against WCAG 2.1 AA and AAA standards for normal text, large text, and UI components. All computations and data processing are executed 100% locally on your device using client-side WebAssembly, HTML5 Canvas, and modern Web APIs without uploading files to any external server.

Supported Formats

WCAG Color Contrast Checker supports the following file formats:

  • HEX — client-side processing support.
  • RGB — client-side processing support.

How to Use WCAG Color Contrast Checker in Browser

  1. Input Colors: Enter foreground text color and background color using the pickers or HEX inputs.
  2. Review Score: Check the exact contrast ratio (e.g. 14.2:1) and AA/AAA compliance status.
  3. Test Live: Inspect the live simulated sample cards to verify visual readability.

Key Features & Privacy Protections

  • 100% Client-Side Privacy: Zero cloud upload. Your documents, photos, and files never leave your local browser sandbox.
  • Zero Installation: Runs instantly in Chrome, Safari, Firefox, Edge, Android, and iOS browsers.
  • Free Forever: No sign-up, no subscriptions, no ads, and no file size limits.

Frequently Asked Questions (FAQ)

What is the minimum WCAG contrast ratio for normal text?

WCAG Level AA requires a minimum ratio of 4.5:1 for body text (under 18pt), while Level AAA requires 7.0:1.

What is the requirement for large text and buttons?

Large text (18pt+ or 14pt bold) and user interface components require a minimum ratio of 3.0:1 for Level AA.

How is relative luminance calculated?

Calculated using the official W3C relative luminance formula based on linear sRGB color space channels.

Can I swap the foreground and background colors?

Yes, click the swap button to invert foreground and background colors with a single click.

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WCAG Color Contrast Checker

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v1.0.0Free · WCAG 2.1 FormulaDeveloper Tools

WCAG Color Contrast Checker Online Free — Accessibility Contrast Ratio Tool

Verify color accessibility and WCAG AA/AAA compliance for text and UI elements.. Calculate color contrast ratios and evaluate accessibility against WCAG 2.1 AA and AAA standards for normal text, large text, and UI components.

What is Contrast Checker and what does it do?

The WCAG Color Contrast Checker is an accessibility testing tool that evaluates color combinations against official Web Content Accessibility Guidelines (WCAG 2.1) Level AA and Level AAA standards.

It calculates exact mathematical contrast ratios, provides instant pass/fail badges for normal body text, large headlines, and UI components, and includes live interactive sample previews.

  • Calculate precise contrast ratios (e.g. 14.2:1) following the official W3C relative luminance formula.
  • WCAG 2.1 compliance matrix: instant Pass/Fail ratings for Level AA (4.5:1) and Level AAA (7.0:1) on normal text.
  • Specific evaluation for Large Text (3.0:1 AA / 4.5:1 AAA) and graphical UI components / button borders (3.0:1 AA).
  • One-click Swap Colors button to test foreground and background color inversions instantly.
  • Live sample canvas previewing headlines, body paragraphs, interactive buttons, and inverted badges.

How does Contrast Checker work?

Hexadecimal color values are converted into linear sRGB color channels. Relative luminance is calculated using the W3C formula: L = 0.2126*R + 0.7152*G + 0.0722*B.

The contrast ratio is computed as (L1 + 0.05) / (L2 + 0.05), where L1 is the lighter luminance. The ratio is compared against WCAG threshold thresholds to generate compliance badges.

100% private: all processing happens locally in your browser using client-side WebAssembly, HTML5 Canvas, and modern Web APIs. Your files are never uploaded to any server.

Who needs Contrast Checker?

Accessibility (a11y) Specialists

Audit digital products for ADA, Section 508, and European EN 301 549 compliance to ensure universal accessibility.

UI/UX Designers

Verify brand color palettes, button styles, and typography tokens before handing design files to developers.

Frontend Developers

Ensure web applications meet accessible contrast standards during design system and theme implementation.

Government & Enterprise Teams

Comply with mandatory public-sector accessibility regulations across portals and customer-facing web apps.

Supported file formats

WCAG Color Contrast Checker processes the following file extensions and data formats directly in your browser:

HEXRGB

How to use Contrast Checker — step by step

  1. 1

    Input Colors

    Enter foreground text color and background color using the pickers or HEX inputs.

  2. 2

    Review Score

    Check the exact contrast ratio (e.g. 14.2:1) and AA/AAA compliance status.

  3. 3

    Test Live

    Inspect the live simulated sample cards to verify visual readability.

Frequently asked questions

What is the minimum WCAG contrast ratio for normal text?

WCAG Level AA requires a minimum ratio of 4.5:1 for body text (under 18pt), while Level AAA requires 7.0:1.

What is the requirement for large text and buttons?

Large text (18pt+ or 14pt bold) and user interface components require a minimum ratio of 3.0:1 for Level AA.

How is relative luminance calculated?

Calculated using the official W3C relative luminance formula based on linear sRGB color space channels.

Can I swap the foreground and background colors?

Yes, click the swap button to invert foreground and background colors with a single click.

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