What is the WOFF file format?
WOFF (Web Open Font Format) is an open format for storing web fonts, developed in 2009. .woff files contain fonts compressed with zlib, wrapping TrueType (.ttf) and OpenType (.otf) outlines in a compact binary container. The format supports embedded font licensing metadata, which many commercial fonts require for legal web use.
.woff files are used for deploying custom fonts for websites. WOFF is the most common font format used by web designers, and open standard status combined with full support across modern web browsers are the main reasons for its widespread adoption.
The WOFF format was designed with two goals in mind. The first goal was to distinguish fonts for websites from those used by locally installed applications, which use fonts installed on the local disk. The second goal was to reduce web font latency when fonts are transferred from a server to a client.
.wofffiles are referenced within CSS files using the@font-facerule.- The format was later succeeded by WOFF2, which replaces zlib with Brotli compression for roughly 30% smaller file sizes.
Security & safety
RISK: LOWA WOFF file is font data, not executable code, so it is safe to handle. The realistic risk is font-parser vulnerabilities (the OS/browser font-rendering engine has a CVE history), so keep your browser and system patched and obtain fonts from reputable foundries. Also mind licensing: many web fonts are licensed for web embedding only - converting a WOFF to TTF and installing it for desktop use may violate the font's license even though it is technically easy. Beware sketchy 'free font' sites that bundle adware in their downloaders; use the converter directly rather than an installer.
Format details
in a nutshellPrograms that open WOFF files
Windows3 apps
FontForge
Open-source File > Open the .woff to inspect glyphs; File > Generate Fonts to export TTF/OTF for installing. 
Web browser (Chrome/Firefox/Edge)
Free Browsers consume WOFF via @font-face automatically; not a previewer, but confirms the font renders on the web.
Transfonter (web)
Free Upload the .woff to preview it and convert to/from TTF/OTF/WOFF2 in the browser. 
macOS2 apps
Linux2 apps
fontTools (Python)
Open-source Command line: decompress WOFF/WOFF2 to TTF/OTF (pip install fonttools brotli).
Transfonter / online font converters
Free Drag a .woff in to preview and convert client-side; good for one-off TTF extraction. Technical details
deep spec| Format type | Binary wrapper repackaging compressed sfnt (TrueType/OpenType) font tables |
| MIME type | font/woff |
| File signature | ASCII `wOFF` (hex `77 4F 46 46`) at byte offset 0 |
| Compression algorithm | zlib (DEFLATE); each sfnt table is compressed independently |
| Wrapped font flavors | TrueType-flavored (sfnt flavor `00 01 00 00`) or CFF/OpenType-flavored (`OTTO`) |
| WOFF header size | Fixed 44-byte header storing signature, sfnt flavor, file length, and table count |
| Per-table directory | Each entry stores compressed size, original uncompressed size, and file offset |
| Licensing metadata | Optional compressed XML metadata block for author, copyright, and license declarations |
| Private data block | Optional unstructured binary block at end of file reserved for font creator use |
| CSS integration | Declared via `@font-face` at-rule; the browser fetches and caches the file automatically |
| Glyph data integrity | Repackages existing font tables without altering glyph outlines or hinting data |
| Browser support | Universally supported in Chrome, Firefox, Safari, and Edge since 2012 |
| Successor format | Superseded by `.woff2`, which uses Brotli compression for roughly 30% smaller files |
| Tooling | Convertible with `fonttools` (Python), FontForge, or web services such as Transfonter |
| Released | 2009; W3C Recommendation December 2012 (WOFF 1.0) |
| Open standard | Yes · royalty-free |
| Specification | www.w3.org |
WOFF conversions
Community Q&A
asked by usersNo questions yet - be the first to ask about WOFF files.
