This web utility calculates contrast ratios and WCAG grades for a pair of colors, then simulates how those colors are perceived by people with a range of visual impairments (various forms of color blindness, cataracts, glaucoma, low vision) and situational conditions like direct sunlight or night-shift mode.

The tool uses established libraries (for example, Chroma.js for contrast math and a color-blind simulation plugin) alongside custom simulations for conditions such as cataracts and low vision. Population estimates shown are drawn from public sources to give context to who might be affected and how severely.

Grades are determined by contrast plus typographic factors (font size and weight); a failing grade indicates potential visual strain for affected users. The project is open source, maintained by Corey Ginnivan, and accepts forks and pull requests for improvements.