Project 48, Developer tools

Regex Tester

Type a pattern and watch matches light up in your text. Groups, replacements and a plain-English explanation update as you type.

Engine: JavaScript RegExp
Flags: g i m s u y d v
Dependencies: None
Your browser: Checking

Pattern

//g

Test text

Replace with

Matches

What your pattern means

Common patterns

Cheat sheet

How it works

Build the RegExpThe pattern and flags make a new RegExp. A syntax error is shown instead of crashing.
Find matches safelymatchAll runs inside a Worker. If a pattern takes more than a second, the worker is stopped so the page never hangs.
Show resultsMatch positions become highlighted spans. Groups fill the table and the replace preview runs on the same text.

const re = new RegExp(pattern, "gd");            // d = give match indices
for (const m of text.matchAll(re)) {
  console.log(m[0], m.index, m.groups);           // full match, where, named groups
  console.log(m.indices[1]);                      // start and end of group 1
}
// Stop runaway patterns like /(a+)+$/ from freezing the page
const w = new Worker(url); w.postMessage({ pattern, flags, text });
const t = setTimeout(() => { w.terminate(); showError("Too slow, stopped"); }, 1000);