Tool Fu
$ toolfu run regex-tester

Regex Tester — Test Regular Expressions Online

Free online regex tester and debugger. Test regular expressions with real-time matching, highlighted results, and capture groups. Try regex online instantly — runs in your browser.

all processing runs in your browser
regex-tester
pattern > regex
//g
flags:
test string
2 matches found
Contact us at hello@example.com or support@toolfu.dev for help.
#0"hello@example.com"@14
#1"support@toolfu.dev"@35

Test Regular Expressions Online — Free Regex Tester

This free online regex tester lets you test regular expressions with real-time matching, highlighted results, and detailed capture group output. Write a regex pattern, set flags, and see matches highlighted instantly — try regex online without installing anything.

Enter your regular expression, toggle flags (global, case-insensitive, multiline, dotall), and type your test string. The regex tester highlights matches in the output and lists each match with its position and captured groups. This regular expression testing tool runs entirely in your browser using JavaScript's built-in RegExp engine.

Online regex tester features

  • Test and debug regex patterns with real-time visual feedback
  • Try regex online with all JavaScript flags (g, i, m, s)
  • Extract data from text using capture groups and named groups
  • Validate regular expression patterns for forms and data processing
  • Web regex tester that runs privately — no data sent to any server
$ cat FAQ.md
What regex flavor does this tool use?▶
This tool uses JavaScript's built-in RegExp engine, which supports standard regex syntax including character classes, quantifiers, groups, lookahead/lookbehind, and named capture groups. The syntax is ECMAScript-compatible.
What do the flags mean?▶
g (global) finds all matches instead of stopping at the first. i (case-insensitive) ignores case when matching. m (multiline) makes ^ and $ match line boundaries instead of just the start/end of the string. s (dotall) makes the dot (.) match newline characters as well.
Is my data sent to a server?▶
No. All regex matching happens entirely in your browser using JavaScript's RegExp. Your patterns and test strings never leave your device.
Is there a limit on the number of matches?▶
The tool limits results to 10,000 matches to prevent browser hangs from patterns that produce extremely large numbers of matches. For most use cases, this limit is more than sufficient.