What Is the SIL Open Font License?
The SIL Open Font License (OFL) is the most widely used open-source license for fonts. Created by SIL International, it enables font designers to release their work freely while protecting the integrity of the original design.
Fonts under the OFL include Inter, Roboto, Open Sans, Lato, Montserrat, Poppins, and hundreds of others on Google Fonts.
What the OFL Allows
You are free to:
- ✅ Use the font for any purpose — personal, commercial, government
- ✅ Embed the font on websites, in apps, and in documents
- ✅ Modify the font — create derivatives, add characters, adjust spacing
- ✅ Distribute the font — share it with others, include it in products
- ✅ Subsetting — reduce the character set for web performance
- ✅ Convert formats — TTF to WOFF2, etc.
What the OFL Requires
Compliance is simple but non-negotiable:
- Include the license text — the OFL must accompany the font when distributed
- Preserve copyright notices — do not remove author attributions embedded in the font
- Reserved font names — if you modify a font, you cannot use its original reserved name (defined in the font's OFL header) unless you have written permission
What the OFL Prohibits
- ❌ Selling the font by itself — you cannot package Inter.woff2 and sell it as a standalone product
- ❌ Using reserved names on derivatives — a modified Roboto cannot still be called "Roboto"
These restrictions protect font designers' work while keeping the fonts free for normal use.
OFL vs. Other Open Licenses
| License | Used By | Key Difference |
|---|---|---|
| SIL OFL 1.1 | Google Fonts (majority) | Font-specific; reserved names clause |
| Apache 2.0 | Some Google Fonts | General open-source; patent grant included |
| MIT | Some indie fonts | Minimal restrictions; no reserved names |
| GPL | Rare for fonts | Copyleft; derivatives must also be GPL |
For website use, all of these are generally safe for commercial projects.
Common OFL Misconceptions
"Open source means I can do anything." You can use OFL fonts commercially, but you still cannot sell the raw font files or misrepresent modified versions as the original.
"I need to credit the designer on my website." Attribution is appreciated but not required by the OFL for normal use. It is required when redistributing the font files themselves.
"OFL fonts are lower quality." Many OFL fonts match or exceed commercial alternatives. Inter, designed by Rasmus Andersson, is used by GitHub, Mozilla, and Figma.
When OFL Fonts Are Not Enough
The OFL covers the font itself, but your website may still load non-OFL fonts alongside open-source ones. A site using Inter (OFL) and Helvetica (commercial) is only compliant for Inter. Always audit the complete font stack.
Conclusion
The SIL Open Font License makes high-quality typography accessible to everyone. Understand its simple rules, use OFL fonts confidently, and scan your site to ensure no unlicensed commercial fonts have crept in alongside them.