WOFF2 Font MIME Type

What does font/woff2 mean?

The font/woff2 media type identifies a Web Open Font Format 2.0 resource. A .woff2 file packages an sfnt-based font, usually TrueType or OpenType, for efficient delivery to a web browser. It preserves the font's glyphs, character mappings, metrics, layout features, variation data, and other supported tables while representing them in a more compact transport format.¹²

WOFF2 is a container, not a new kind of outline. Two .woff2 files can enclose very different fonts, including TrueType outlines, CFF outlines, variable fonts, color fonts, or a font collection. A browser decodes the package before its font and text-shaping systems use those tables.²

How to identify a WOFF2 file

Every valid WOFF2 file starts with the four-byte signature 77 4F 46 32, which spells wOF2 in ASCII. The W3C specification assigns this value as 0x774F4632 and requires a user agent to reject a file whose signature does not match.²

The 48-byte header also records the underlying sfnt flavor, the file length, the number of font tables, compressed and reconstructed sizes, version fields, and offsets for optional metadata and private-data blocks. The signature identifies the container, but the header and table directory must still be validated. A filename ending in .woff2 is not proof that the data is a valid font.²

IANA lists one registered extension, .woff2, and no required or optional media-type parameters. Serve the file as Content-Type: font/woff2 rather than application/octet-stream or an old application/x-font-* label.¹ Poly also recognizes the legacy application/font-woff2 label, but it is not a separate registered type or format.

Where WOFF2 came from

The W3C WebFonts Working Group published the first public WOFF2 draft on May 8, 2014. The format reached Candidate Recommendation in 2016 and became a W3C Recommendation on March 1, 2018.³ RFC 8081 had established the dedicated font top-level media type and registered font/woff2 in February 2017.⁴

WOFF2 built on WOFF 1.0, which used per-table Flate compression. Its designers wanted smaller transfers without imposing excessive decoding cost on mobile devices. WOFF2 first restructures selected font tables to remove or compact redundant information, then compresses the combined table stream with Brotli. Decoding reconstructs a functionally equivalent sfnt font, although transformed tables need not be byte-for-byte identical to the original representation.²⁵

How much smaller is WOFF2 than WOFF?

File-size savings depend on the source font, its outline technology, its tables, and the encoder. W3C reported results from three development datasets: about 1,100 TrueType fonts from Google Fonts, 33,000 TrueType fonts from Monotype, and an Adobe corpus of 13,900 TrueType plus 5,000 CFF fonts. In that evaluation, every tested WOFF2 output was smaller than its WOFF 1.0 counterpart.⁵

These figures describe those corpora and the encoders used during WOFF2 development. They are not a guaranteed saving for an individual font. Subsetting away unused characters can have a larger effect than changing containers, while a small or already carefully optimized source may show a smaller difference.

How to use a .woff2 file in a website

Current Chrome, Edge, Firefox, Opera, and Safari can load WOFF2 through CSS @font-face. MDN describes WOFF2 as the normal web-delivery choice because it combines efficient compression with broad modern-browser support.⁶

@font-face {
  font-family: "Example Sans";
  src: url("/fonts/example-sans.woff2") format("woff2");
  font-style: normal;
  font-weight: 100 900;
  font-display: swap;
}

Return Content-Type: font/woff2. If the font is hosted on a different origin from the page, configure an appropriate CORS response because web fonts are subject to cross-origin access controls.⁶

Opening a .woff2 URL directly may download the file or show a browser's generic resource view. The reliable way to inspect its appearance is to reference it from a small HTML and CSS specimen. For table-level inspection, first decode it with a trusted font-aware tool, then validate the reconstructed font. Browser developer tools can confirm whether the request succeeded and which face was actually used.

Support in Poly

Poly previews .woff2 fonts with a type specimen, shows face details, and lets you find files by filename or visual similarity. The details panel shows the family, format, weight, style, monospaced and variable-font status, face and glyph counts, and estimated language coverage. These fields are not full-text indexed.

The Poly agent can inspect the specimen image and a caption with the family, format, glyph count, and language coverage. Poly processes the first face of a collection and uses default variation settings, so the preview and agent view do not show other faces or alternate variable-font axis positions. Use a font editor or a web specimen when you need those details or want to inspect the underlying tables.

WOFF2, WOFF, TTF, and OTF compared

These formats are closely related, but they serve different delivery and authoring roles.

WOFF2 and WOFF can be offered in parallel because they have different MIME types. For modern browser targets, WOFF2 is normally sufficient. A WOFF fallback matters only when a project's compatibility requirements include browsers without WOFF2 support.²⁶

Converting and subsetting WOFF2

Use a font-aware encoder or decoder rather than a general archive utility:

• TTF or OTF to WOFF2: creates a web-delivery copy. Check that the license permits web embedding and conversion.
• WOFF2 to TTF or OTF: reconstructs an sfnt font for inspection or editing. The decoded tables may be functionally equivalent without matching the original source bytes.²
• WOFF2 to WOFF: useful only for an older-browser fallback. Decode and re-encode with a font tool; renaming the suffix is not conversion.
• Subsetting: removes unused characters and possibly layout data. It can save substantial bandwidth, but missing characters fall back to another face and damaged shaping tables can break complex scripts.

Generate separate subsets only when the CSS unicode-range values and fallback behavior are well tested. Keep the full licensed source so you can regenerate files when language coverage or browser requirements change.

Security, privacy, and licensing

WOFF2's compression does not make an untrusted font safe. Fonts contain complex tables, and TrueType hinting can include interpreted instructions. RFC 8081 warns that malicious fonts can consume excessive CPU or memory and that extensible font structures can conceal arbitrary binary content.⁴

WOFF2 may also contain extended metadata and an arbitrary private-data block. Font formats do not provide confidentiality, so inspect these areas before publishing a proprietary or commissioned font.²⁴ Finally, compression, conversion, and subsetting do not grant a web-font license. Confirm that the license permits hosting, modification, and redistribution before deploying the file.