Regex Colorizer is a lightweight library (3.8 kB, with no dependencies) for adding syntax highlighting to your regular expressions in blogs, docs, regex testers, and other tools. It supports the JavaScript regex flavor (ES2023) with web reality. In other words, it highlights regexes as web browsers actually interpret them.

The API is simple. Just give the elements that contain your regexes (pre, code, or whatever) the class regex, and call colorizeAll(). See more usage examples below.

Errors are highlighted, along with some edge cases that can cause cross-browser grief. Hover over errors for a description of the problem.

Try it out on the demo page, which also includes more details.

npm install regex-colorizer

import {colorizeAll, loadStyles} from 'regex-colorizer';

<script src="https://cdn.jsdelivr.net/npm/regex-colorizer/dist/regex-colorizer.min.js"></script>
<script>
  const {colorizeAll, loadStyles} = RegexColorizer;
</script>

import {colorizeAll, colorizePattern, loadStyles} from 'regex-colorizer';
// Don't run this line if you provide your own stylesheet
loadStyles();
// Highlight all elements with class `regex`
colorizeAll();
// Or provide a `querySelectorAll` value for elements to highlight
colorizeAll({
  selector: '.regex',
});
// Optionally provide flags
colorizeAll({
  // Flags provided in `data-flags` attributes will override this
  flags: 'u',
});
// You can also just get the highlighting HTML for a specific pattern
element.innerHTML = colorizePattern('(?<=\\d)', {
  flags: 'u',
});

In your HTML:

<p>
  This regex is highlighted inline:
  <code class="regex">(?&lt;=\d)\p{L}\8</code>.
  And here's the same regex but with different rules from flag u:
  <code class="regex" data-flags="u">(?&lt;=\d)\p{L}\8</code>.
  <!-- Can include any valid flags. Ex: data-flags="gimsuyd" -->
</p>

Several themes are available as stylesheets, but you don't need to add a stylesheet to your page to use the default theme. Just run loadStyles().

Regex Colorizer was created by Steven Levithan. It started in 2007 as part of RegexPal, the first web-based regex tester with regex syntax highlighting. It was extracted into a standalone library in 2010.

If you want to support this project, I'd love your help by contributing improvements, sharing it with others, or sponsoring ongoing development.

© 2007–present. MIT License.