Small, efficient encoding of SVG data URIs for CSS, HTML, etc.
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Latest commit 2304df6 May 29, 2018

README.md

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='http://www.w3.org/2000/svg' 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

Compare to the Base64 version (210 bytes):

data:image/svg+xml;base64,PHN2ZyB4bWxucz0iaHR0cDovL3d3dy53My5vcmcvMjAwMC9zdmciIH
ZpZXdCb3g9IjAgMCA1MCA1MCI+PHBhdGggZD0iTTIyIDM4VjUxTDMyIDMybDE5LTE5djEyQzQ0IDI2ID
QzIDEwIDM4IDAgNTIgMTUgNDkgMzkgMjIgMzh6Ii8+PC9zdmc+

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

data:image/svg+xml;charset=US-ASCII,%3Csvg%20xmlns%3D%22http%3A%2F%2Fwww.w3.org%
2F2000%2Fsvg%22%20viewBox%3D%220%200%2050%2050%22%3E%3Cpath%20d%3D%22M22%2038V51
L32%2032l19-19v12C44%2026%2043%2010%2038%200%2052%2015%2049%2039%2022%2038z%22%2
F%3E%3C%2Fsvg%3E

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.

Usage

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

var svg = '<svg xmlns="http://www.w3.org/2000/svg" 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='http://www.w3.org/2000/svg' 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.

Warning

  • 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.

FAQ

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