TrueType Font MIME Type

What does font/ttf mean?

The font/ttf media type identifies a TrueType-flavored font. A typical .ttf file is an sfnt container whose tables describe glyph outlines, character mappings, metrics, names, hinting instructions, and possibly advanced layout features. A font renderer scales the outlines and turns them into pixels at the requested size.¹

TrueType is not merely a collection of letter-shaped images. Its glyphs use mathematical outlines, while its tables connect characters to glyphs and tell software how to space and render them. Modern .ttf files are commonly OpenType fonts with TrueType outlines. OpenType deliberately retained the TrueType sfnt container and compatibility with the original TrueType format.²

How to identify a TTF file

The registered signature is the four-byte sfntVersion value 00 01 00 00, also written as 0x00010000. It indicates TrueType outline data. The table directory follows that value and lists the font's top-level tables.²³

Some older Apple TrueType fonts begin with the ASCII tag true instead. The current OpenType specification permits that legacy value in Apple's TrueType model but says OpenType fonts should not use it.² This is one reason a robust identifier should inspect the header and table directory rather than checking only the filename.

RFC 8081 registered font/ttf in February 2017. The media type is therefore much newer than the font technology itself. Before the dedicated font top-level type existed, servers often sent unregistered labels such as application/x-font-ttf or generic application/octet-stream. Those historical labels are not alternate versions of TrueType, and new configurations should use font/ttf.³

Where TrueType came from

Apple designed TrueType as an efficient, extensible outline-font technology and licensed it to Microsoft. Apple shipped full support in System 7 in May 1991. Microsoft followed with Windows 3.1 in April 1992.⁴

The format solved two related problems. One font outline could scale across many screen and printer sizes, and TrueType hinting could adjust those outlines to the pixel grid for clearer rendering at small sizes. OpenType later extended the same container with broader language and typographic capabilities while supporting both TrueType and CFF outline systems.¹⁵

The MIME registration came later because downloadable web fonts had become common. RFC 8081 created the font top-level type and registered font/ttf, font/otf, font/woff, and font/woff2 as clearer labels for the formats already in use.³

How to open or install a .ttf file

On macOS, double-click the file to inspect and install it with Font Book. Font Book supports ordinary and variable TrueType .ttf files and validates fonts for errors during installation.⁶ On Windows 10 or 11, right-click a .ttf file and choose Install, or use Settings > Personalization > Fonts to preview and manage installed fonts.⁷

Current Chrome, Edge, Firefox, Opera, and Safari releases can use TrueType fonts supplied through CSS @font-face. MDN lists font/ttf as the TrueType MIME type and describes @font-face as widely available across browsers.⁸

@font-face {
  font-family: "Example Sans";
  src: url("/fonts/example-sans.ttf") format("truetype");
  font-display: swap;
}

The server should return Content-Type: font/ttf. Cross-origin font requests also need an appropriate CORS response when the font and page come from different origins.⁸

Support in Poly

Poly recognizes the .ttf extension and maps it to font/ttf. It can store, sync, share, version, and find the file by name. The current client classifies TTF as an unknown media category, however, and the indexer sends it through the generic-file path.

That has four practical consequences:

• Poly does not generate a font specimen or thumbnail.
• The preview screen does not render the font. Download it and use Font Book, Windows font settings, or a font editor instead.
• Search covers the filename and ordinary file properties, not family and style names, glyph coverage, OpenType features, or embedded licensing records.
• The Poly agent cannot inspect or reason about the font's internal tables or rendered glyphs.

Changing the filename to .txt, .otf, or an image extension does not enable those capabilities. It only gives Poly and other software misleading type information.

TTF, OTF, WOFF, and WOFF2 compared

These labels overlap because they describe related outline systems and containers, not four unrelated font designs.

RFC 8081 notes that .ttf is typically used for TrueType outlines, while .otf can represent an OpenType font with TrueType or CFF outlines.³ The suffix alone is therefore a convention, not a complete technical description.

WOFF is a wrapper around an existing TrueType or OpenType font. A conforming WOFF decoder restores the underlying font data so it renders identically to its well-formed input.⁹ WOFF2 applies additional transformations before compression to remove redundancy in the sfnt representation.¹⁰

Converting a TTF file

Choose the output for the job:

• TTF to WOFF2: best for serving a font on the web. Use a font-aware converter, retain the original, and verify that names, glyphs, variable axes, and layout features survived.
• TTF to WOFF: useful as a compatibility fallback. WOFF repackages the font tables rather than redesigning the glyphs.⁹
• TTF to OTF: useful only when a tool or production workflow specifically requires an .otf deliverable. Renaming the file is not conversion, and changing outline formats can alter hinting or other details.
• TTF to a subset: reduces a web font to selected glyphs, but omitted characters will fall back to another font. Test every language, symbol, and OpenType feature your page needs.
• TTF to PDF or images: appropriate when you need to preserve a particular appearance without distributing an installable font. The result is no longer a reusable font file.

Check the font license before converting, subsetting, embedding, or redistributing it. A technically successful conversion does not grant permission to publish the result.

Are TTF files safe?

Treat an untrusted font as executable input to a complex parser. TrueType hinting instructions are interpreted code, and RFC 8081 warns that malicious fonts can consume excessive CPU or memory. The extensible table structure can also carry hidden binary data.³

Fonts can also contain names, copyright notices, vendor details, and licensing permissions. They do not provide confidentiality for that information. Inspect those fields before distributing an internal or commissioned font.¹³