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You're building a website and need to serve custom fonts. The format you want is WOFF2. It wraps TrueType or OpenType font data in Brotli compression, producing files 30–50% smaller than uncompressed fonts — which translates directly to faster page loads and better Core Web Vitals scores.
Every modern browser supports WOFF2: Chrome, Firefox, Safari, Edge. The font data inside is identical to TTF or OTF; WOFF2 just compresses it for delivery over HTTP. The older WOFF (version 1) used zlib compression and is still supported as a fallback, but there's no reason to serve WOFF over WOFF2 unless you're targeting Internet Explorer 11. For font subsetting (including only the characters you actually use), tools like Glyphhanger and pyftsubset can dramatically reduce file size further.
FontForge (free) can convert TTF/OTF to WOFF2. Google Fonts serves WOFF2 by default. Most font foundries provide WOFF2 webfont files with their licences. If you're self-hosting fonts, serve WOFF2 with a font-display: swap declaration for the best performance. That's the entire modern web font stack — everything else is legacy.