Font Performance Checker
Analyse font files for web performance. Detects the actual format from magic bytes, measures file size, and recommends specific optimizations — WOFF2 conversion, subsetting, or confirm the font is already optimized.
What the performance checker analyses
- Real format — detected from file signature, not extension. A TTF renamed to
.woff2is still a TTF. - File size — with context for what "small" and "large" mean for web fonts.
- Compression state — WOFF and WOFF2 are pre-compressed; TTF and OTF are not.
- Recommendation — specific next step based on format and size.
File size benchmarks for web fonts
| Size | Assessment | Action |
|---|---|---|
| Under 50KB | Excellent | Ship as-is |
| 50–100KB | Good | Ship as-is, consider subsetting |
| 100–200KB | Acceptable | Subset if possible |
| 200–400KB | Large | Subset required |
| Over 400KB | Too large | Replace or heavily subset |
Remember: The file size shown is what the browser downloads on first load. With proper cache headers (
max-age=31536000, immutable), this cost is paid once per user — not per page visit. But on mobile connections, even one 400KB font can significantly delay LCP.Frequently asked questions
How do I check if my font is optimized?
Upload the font file to this tool. It reports the actual format, file size, and recommends specific actions.
What is a good font file size for web?
Under 100KB per WOFF2 file is good. Under 50KB is excellent. Over 200KB should be subsetted further or replaced.
Can I analyse fonts hosted on a URL?
Not in this tool — cross-origin restrictions prevent fetching arbitrary font URLs. Download the font file and upload it here.
Does the checker modify my files?
No. Files are read locally in your browser to determine format and size. Nothing is uploaded to a server.