Users should be able to read and understand the information presented by your application. Your application should also be flexible enough to meet your user's reading needs. Check in particular:
- Can the page be resized to 200% in the browser and still be usable?
- Are text sizes appropriate across variable device widths?
- Can the page still be read if the user is overriding your fonts with their own? (Try testing this using the Chrome addon OpenDyslexic)
- Does the text need to be adjusted for colour or weight to provide adequate contrast? (Try your most used fonts in a contrast checker)