Why it matters
Computes size-adjust and ascent, descent and line-gap overrides so fallback fonts match your web font and reduce layout shift.
Parses OS/2 and hhea metrics and average character width (xAvgCharWidth or measured from cmap/hmtx over a weighted Latin sample) from the uploaded font; bundled metrics for common system fallbacks; outputs @font-face fallback blocks; overlay preview of text reflow. Shares the OpenType parser with font-subset-estimator. Everything runs in your browser; nothing you paste is sent unless you press Fetch.
How to use it
- Paste or type the input the tool asks for.
- Read the summary and the table or preview.
- Adjust the options if you need a different result.
- Copy or download the output. Nothing leaves this page.
FAQ
Is my input uploaded?
No. The work runs in your browser and nothing you type, paste or upload is sent anywhere.
Will this change my site for me?
No. It shows results and, where it writes rules or files, you copy them and apply them yourself.
Can I rely on this as official guidance?
It follows public documentation and well-known algorithms, and tells you where it is a subset or a simulation. Confirm critical changes in the official tool or a staging environment.
