UI Fonts is a small free web tool that lets you preview typefaces inside realistic interface mockups instead of an isolated paragraph. You pick a font (from Google Fonts and other free libraries), and the page swaps it into pre-built UI scenes — settings panels, dashboards, sign-up forms, marketing sections — so you can see how it actually feels at button, label, and heading sizes.

There's a side-by-side compare mode for evaluating two candidates at once, and links out to the source library when you've decided. It's a one-job utility for the moment of choosing typography for a product, and stays free with no signup.