WhatFont is a Chrome extension, with an unofficial but Mozilla-listed Firefox port, that tells you the exact font, weight, size, and color of any text you hover over on any page.
One hover surfaces what would otherwise mean digging through computed styles in devtools, including whether the font is served via Typekit or Google Fonts, without opening the inspector at all.
Grab it when a client says "use whatever font that other site is using," or when you're rebuilding a shipped page and need to confirm your CSS actually matches what's rendering in production, not merely what's in the stylesheet.
It's been a stable, low-permission tool for over a decade (3 million users, and the developer states data is neither collected nor sold), so staleness risk is low; just note the Firefox build is a community port, not the original developer's.
The easiest way to identify fonts on web pages.
