WAVE Evaluation Tool
Accessibility Checker: Test WCAG 2.1 & Section 508 Compliance
WAVE Web Accessibility Tool
Contrast Ratio: Easily calculate color contrast ratios. Passing WCAG was never this easy!
Contrast for UI
Koa11y Download
WCAG 2.0 Standard: Summary - HTML_CodeSniffer
Pa11y - Your automated accessibility testing pal
tota11y – an accessibility visualization toolkit by Khan Academy