FILE FORMAT GUIDE
OpenType CFF Font (.OTF): Tables & Safe Inspection
An OTF file conventionally packages OpenType tables with CFF or CFF2 outline data. OpenType layout tables may describe advanced script and typographic behavior.
Check supported header evidence locally. Identification is not file validation or a malware scan.
Analyze a file locallyQuick 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
- fontTools TTFont
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.
- Store a table-based font for use by supporting font systems
How to open OTF
Inspect tables without installing the font. Loading untrusted files into any parser remains separate from deciding whether the font is safe or licensed for use.
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
Things to check
- Parsing a font does not grant permission to install, modify or redistribute it.
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
Fact review: 2026-09-19. Unknown fields are not inferred from the file extension.