Accessibility
Web accessibility is extremely important for anyone visiting your site! Readable color contrast, spacing, and formatting make sure that everyone is able to view your site to the fullest.
Now there is a lot more to accessibility than just what these tools can test, but this will help with some main features.
Test Your Accessibility
Wave: https://wave.webaim.org/
Browser extensions: https://wave.webaim.org/extension/
This is probably the easiest, as you can view directly on the page where your errors are!
Contrast Checker: https://webaim.org/resources/contrastchecker/
Wonderful tool to help check if the color contrast on your site is accessible!
Accessibility Checker: https://www.accessibilitychecker.org
Accessibility Widget
UserWay offers a free widget to help users adjust websites to their viewing preferences, such as fonts, sizing, spacing, and more. This does not replace the accessibility requirements above!!!
You can find the free version of the widget at https://userway.org/compare/ (click Get Free Widget)