Free Regex Tester
Regex Tester runs JavaScript regular expressions against your text with live highlighting, capture groups and all eight flags. A replace preview supports $1, $<name> and $&, and an explainer describes the pattern in plain English. Matching runs in a background worker that stops after 1 second, so catastrophic backtracking cannot freeze the tab.
- Flavor:
- JavaScript (ECMAScript)
- Flags:
- g, i, m, s, u, y, d, v
- Time limit:
- 1 second per match run
- Price:
- Free
- Runs:
- Locally, in your browser
- Uploads:
- None: files never leave your device
- Account:
- Not needed
Quick answers
Which regex flavor is used?
Your browser's own JavaScript (ECMAScript) engine, so results match what your code will do in Chrome, Firefox, Safari or Node.js.
Processed on your device: your files are never uploaded. How it works
Network activity in this tab
What this page has requested since you opened the site in this tab. An upload is any request that sends data: POST, PUT, PATCH or a request with a body.
No uploads: nothing has been sent from this page.
No network requests yet.
To see every request, open your browser's developer tools (Network tab).
How to use the Regex Tester
- Type a pattern and toggle the flags you need (g, i, m, s, u, y, d, v), or insert one from the common patterns list.
- Paste your test text: matches are highlighted live and listed with their groups.
- Open Replace to preview a replacement with $1, $<name> or $&, or Explain to read the pattern in plain English.
Credits & open source
Our own code plus open-source libraries. Thank you to the people who make these projects.
- regexp-treeRegular expression parser used to explain patterns in words. © Dmitry Soshnikov · MIT
Web platform APIs used: Web Workers, Clipboard API.
Full license texts: third-party notices · all credits
Frequently asked questions
What happens with a pattern that hangs?
Matching runs in a background worker with a 1-second limit. If the pattern backtracks catastrophically, the worker is stopped and you get a warning instead of a frozen tab.
Is my test text sent anywhere?
No. Everything runs locally in your browser.