Font sizes smaller than 12px are often difficult to read on mobile devices, and may require users to pinch-to-zoom in order to display the text at a comfortable reading size.
Aim to have a font size of at least 12px on at least 60% of the text on your pages. When a page fails the audit, Lighthouse lists the results in a table with 4 columns:
- Source. The source location of the CSS ruleset that is causing the illegible text.
- Selector. The selector of the ruleset.
- % of Page Text. The percentage of text on the page that is affected by the ruleset.
- Font Size. The computed size of the text.
Text is illegible because of a missing viewport config
If Lighthouse reports
Text is illegible because of a missing viewport config, add a
<meta name="viewport" content="width=device-width, initial-scale=1"> tag to the
your document. See Has A Viewport Meta Tag With Width Or Initial-Scale.