Sources:
https://medium.com/bread-crumbs/free-web-accessibility-tools-round-up-b83a33797789#.phl56t1kk
AxE
Analyze a site for accessibility violations and warnings. aXe will let you know how serious the violation is, what WCAG guideline is being violated, and details about the element in question.
Color Contrast Analyzer
Add a mask to your page with a visual map of contrast. Everything that doesn’t have white outlines is not compiant
WAVE Evaluation Tool
Really nice, feature rich and quick. Shows the results inline. Also shows color contrast problems and how to fix them
Colour Contrast Check
Web tool for analyzing contrast of 2 colors against 4 WCAG modes