autosubset – Automatically subset a font based on actual text

autosubset creates a subset font exactly for the set of characters that you actually use.

Usage

Just pipe the text into autosubset and specify the font.

Assuming all your text is in the HTML files in the current directory:

html2text *.html | autosubset.py MyFont.woff2

autosubset analyzes the content, extracts the characters used and uses pyftsubst from fonttools to create a matching subset.

After that, just add lines like the following to your web site:

• HTML: Preload the font for faster availability.

  <link rel="preload" href="MyFont.subset.woff2" as="font" type="font/woff2">

• CSS: Define and use the font.

  @font-face {
    font-family: "My Font";
    src: local("Tenor Sans"), url("MyFont.subset.woff2") format("woff2");
    font-display: fallback;
  }
  @body {
    font-family: "My Font", "System Fallback Font", sans;
  }

Whenever you change your text, make sure to rerun autosubst. This ensures that the browser does not need to substitute characters from the fallback fonts.