Small, efficient encoding of SVG data URIs for CSS, HTML, etc.
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tigt Fix: hex color regex too lazy
Previously, hex codes like "#000def" would get changed into
"blackdef". Turns out regular expressions are subtle and tricky
Latest commit 2304df6 May 29, 2018

Mini SVG data: URI

This tool converts SVGs into the most compact, compressible data: URI that SVG-supporting browsers tolerate. The results look like this (169 bytes):

data:image/svg+xml,%3csvg xmlns='' viewBox='0 0 50 50'
%3e%3cpath d='M22 38V51L32 32l19-19v12C44 26 43 10 38 0 52 15 49 39 22 38z'/%3e

Compare to the Base64 version (210 bytes):


Or the URL-encoded version other tools produce (256 bytes):


For a more realistic example, I inlined the icons from the Open Iconic project into CSS files with the 3 above methods:

Compression Base64 Basic %-encoding mini-svg-data-uri
None 96.459 kB 103.268 kB 76.583 kB
gzip -9 17.902 kB 13.780 kB 12.974 kB
brotli -Z 15.797 kB 11.693 kB 10.976 kB

Roughly 6% smaller compressed, but don't write off the ≈20% uncompressed savings either. Some browser caches decompress before store, and parsing time/memory usage scale linearly with uncompressed filesize.


var svgToMiniDataURI = require('mini-svg-data-uri');

var svg = '<svg xmlns="" viewBox="0 0 50 50"><path d="M22 38V51L32 32l19-19v12C44 26 43 10 38 0 52 15 49 39 22 38z"/></svg>';

var optimizedSVGDataURI = svgToMiniDataURI(svg);
// "data:image/svg+xml,%3csvg xmlns='' viewBox='0 0 50 50'%3e%3cpath d='M22 38V51L32 32l19-19v12C44 26 43 10 38 0 52 15 49 39 22 38z'/%3e%3c/svg%3e"

You can also try it in your browser at RunKit.


  • This does not optimize the SVG source file. You’ll want svgo or its brother SVGOMG for that.

  • The resulting Data URI should be wrapped with double quotes: url("…"), <img src="…">, etc.

  • This might change or break SVGs that use " in character data, like inside <text> or aria-label or something. Try curly quotes (“”) or &quot; instead.


Don’t you need a charset in the MIME Type?

charset does nothing for Data URIs. The URI can only be the encoding of its parent file — it’s included in it!

Why lowercase the URL-encoded hex pairs?

It compresses slightly better. No, really. Using the same files from earlier:

Compression Uppercase (%AF) Lowercase (%af)
gzip -9 12.978 kB 12.974 kB
brotli -Z 10.988 kB 10.976 kB

I did say slightly.

Browser support

  • Internet Explorer 9 and up, including Edge
  • Firefox, Safari, Chrome, whatever else uses their engines
  • Android WebKit 3+
  • Opera Mini’s server-side Presto