FILE FORMAT GUIDE
OTF File: What It Is & How to Open It
An OTF file conventionally packages OpenType tables with CFF or CFF2 outline data. OpenType layout tables may describe advanced script and typographic behavior.
Compare the reviewed OpenType / TrueType outlines or OpenType / CFF outlines header signature with the filename in your browser.
Check supported file headersQuick facts
- Extension
- .otf
- Format
- OpenType CFF Font
- Category
- font
- MIME type
- font/otf
- Standard / developer
- Microsoft and ISO/IEC Open Font Format contributors
- Open with
- Font preview / Font Book
What is OTF?
The OTTO scaler tag identifies an OpenType font with CFF data. The filename extension alone is weaker evidence than parsing the SFNT table directory.
How to open OTF
Font preview / Font BookWindows / macOS
Double-click the OTF file to preview it with the system font viewer. Install it only when you trust the source and understand the license.
Common uses and compatibility
- Store a table-based font for use by supporting font systems
Things to check
- Parsing a font does not grant permission to install, modify or redistribute it.
Advanced inspection
These developer and command-line workflows inspect structure or metadata. They are not the default way most people open the file.
fontTools TTFontPython library
Open the file with TTFont("font.otf", lazy=True), inspect keys or selected tables, and close it. Do not call save when the task is read-only. WOFF2 support may require optional dependencies.
Technical details
- Signature
- 4F 54 54 4F (OTTO)
- Encoding
- Not applicable
- Container
- SFNT table container
- Compression
- Table data is not inherently compressed
Related formats
- TrueType Font
TTF commonly identifies TrueType-outline fonts; this OTF record covers OpenType fonts using CFF outlines.
- Web Open Font Format 2
WOFF2 is compressed packaging for web-font delivery and can originate from OpenType font data.
Sources & review
Sources reviewed 2026-09-19.