Awesome Open Source
Awesome Open Source


Regulex is a JavaScript Regular Expression Parser & Visualizer.

Try it now:

This project is under reconstruction!


  • Written in pure JavaScript. No backend required.
  • You can embed the graph on you own site through HTML iframe element.
  • Detailed error message. In most cases it can point out the precise syntax error position.
  • No support for octal escape. Yes it is a feature! ECMAScript strict mode doesn't allow octal escape in string, but many browsers still allow octal escape in regex. In regulex, DecimalEscape will always be treated as back reference. If the back reference is invalid, e.g. /\1/, /(\1)/, /(a)\2/, or DecimalEscape appears in charset(because in this case it can't be explained as back reference, e.g. /(ab)[\1]/, Regulex will always throw an error.

Install for Node.js

npm install regulex

Local Build for Browser

This command will generate bundle dist/regulex.js for browser side:

git checkout legacy
npm install -g requirejs
r.js -o build-config.js


Parse to AST

var parse = require("regulex").parse;
var re = /var\s+([a-zA-Z_]\w*);/ ;


var parse = require("regulex").parse;
var visualize = require("regulex").visualize;
var Raphael = require('regulex').Raphael;
var re = /var\s+([a-zA-Z_]\w*);/;
var paper = Raphael("yourSvgContainerId", 0, 0);
try {
  visualize(parse(re.source), getRegexFlags(re), paper);
} catch(e) {
  if (e instanceof parse.RegexSyntaxError) {
    logError(re, e);
  } else {
    throw e;

function logError(re, err) {
  var msg = ["Error:" + err.message, ""];
  if (typeof err.lastIndex === "number") {
    msg.push(new Array(err.lastIndex).join("-") + "^");

function getRegexFlags(re) {
  var flags = "";
  flags += re.ignoreCase ? "i" : "";
  flags += ? "g" : "";
  flags += re.multiline ? "m" : "";
  return flags;

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