.WOFF2

Introduction

WOFF2 is a compressed wrapper for TrueType and OpenType fonts, made for the web and published as a W3C Recommendation in 2018. It holds the same tables as the original font, compressed together with Brotli, and stores the glyph outlines in a transformed form that compresses better. A WOFF2 file is typically much smaller than the font it came from, and every current browser loads it through CSS @font-face.

The earlier WOFF 1.0, .woff, compressed each table separately with zlib.

Structure

A WOFF2 file is big-endian. It begins with a 48-byte header: the signature wOF2, the version of the original font, the total length, the number of tables, the size the font will have once decoded, the size of the compressed data, a version number, and the location of optional metadata and private data. A table directory follows, written compactly: one flags byte that usually names a known table tag, then lengths stored as variable-length numbers. Then comes a single Brotli stream holding every table, followed by the optional extended metadata, which is compressed XML, and private data.

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