Regex Tester
Test regular expressions with live match highlighting, capture groups and a replace preview.
- No uploads
- No limits
- No signup
- Input:
- Pattern
- Output:
- Matches
- Runs on:
- Your device
- Size limit:
- None
- Account:
- Not needed
How to use Regex Tester
Enter a pattern and flags
Type your regular expression and switch flags like g, i or m on and off. Invalid patterns show an error right away.
Paste your test text
Matches are highlighted as you type, and a table lists every capture group with its position.
Preview a replacement
Add a replacement using $1 or $<name> to see the result, then copy it.
Why Regex Tester on Toolshed
No uploads
Everything runs in this browser tab. Your files never leave your device.
No limits
No file-size caps, no daily quotas. Process as much as your device can handle.
No signup
No account, no email, no watermark.
Frequently asked questions
Why did my pattern time out?
Some patterns, such as nested quantifiers like (a+)+$, take exponential time on certain inputs. Matching runs in a background worker that is stopped after half a second so your page never freezes.
Which regex flavor does this use?
JavaScript (ECMAScript) regular expressions, exactly as your browser runs them, including named groups and lookbehind.
Are my files uploaded anywhere?
No. Regex Tester runs entirely in your browser. Your files are processed on your device and are never sent to a server.
Is there a file size limit?
No fixed limit. The only limit is your device's memory. Very large files work best in a desktop browser.
Is Regex Tester really free?
Yes. There's no account and no watermark. A short optional ad, or a 20-second wait, unlocks each download. That's how we keep it free.
Does it work offline?
Once the page has loaded, processing happens locally, so it keeps working even if your connection drops.