What it does
WhoCanUse compares a text colour with its background and shows simulated views for colour-vision differences, low vision and viewing conditions. Text size and boldness contribute to its contrast grading.
Set the background and text values with the colour inputs or hue, saturation and lightness controls. Enter the text size and choose whether it is bold. The table then shows the pair under its listed simulations, including red-green and blue-yellow colour-vision differences, direct sunlight and night mode.
The colour-blindness views transform the input colours before calculating their ratios. Other simulations, including low vision and sunlight, were created by the tool’s author. Treat them as illustrative models when discussing a design.
The population percentages are estimates for individual conditions, with overlap and incomplete coverage. They are not a count of people who can use your finished interface. The project publishes its code under the MIT licence.
Strengths
- Published code lets developers inspect the simulation methods.
Watch out for
- Simulation grades do not establish usability for an individual person.
Best for
- Discussing a text treatment across different viewing conditions
Sources
- WhoCanUse (Oct 27, 2026)
- WhoCanUse repository (Oct 27, 2026)
- WhoCanUse MIT licence (Oct 27, 2026)