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(.*) Regular Expression Tester & Match Debugger

Test JavaScript regular expressions live: highlighted matches, match positions, capture groups and a cheatsheet.

100% Private (Runs in Browser)

💡 Step-by-Step: How to use RegEx Tester & Debugger

  1. Type your pattern, and flags such as g, i, m, s or u in the flags box.
  2. Enter test text; matches are highlighted as you type.
  3. Below the preview, each match is listed with its index and the value of every numbered and named group.
  4. Open the cheatsheet for common tokens.
RegEx Pattern & Test String
Test String Data
Cheatsheet
.any character except newline\d \w \sdigit, word char, whitespace
[abc] [^abc]one of / none of\D \W \Snot digit / word / space
a* a+ a?0+, 1+, 0 or 1a{2,5}2 to 5 times
^ $start / end (of line with m)\bword boundary
(abc)capture group $1(?<name>abc)named group
(?:abc)group, no capturea|ba or b
(?=a) (?!a)followed / not followed by(?<=a) (?<!a)preceded / not preceded by
Flags: g all matches, i ignore case, m multiline, s dot matches newline, u Unicode
2 matches
Real-Time Matches Preview
JavaScript (ECMAScript) regular expressions

How In-Browser RegEx Testing & Evaluation Works

RegEx Tester & Debugger runs entirely in your browser with JavaScript. There is no sign-up, and whatever you type or open here is processed on your device instead of being sent to a server.

Test Regular Expressions Privately Without Cloud Logging

Developers often test regular expressions against real user data, log lines, emails, or API payloads. Cloud-based regex tools may store your test strings on remote servers. This tester evaluates expressions entirely in your browser using native JavaScript engines, ensuring test data remains strictly on your machine.

Real-Time Match Highlighting and Capture Groups

See matched substrings highlighted instantly as you type your pattern. Inspect each match's start index, its text and its captured groups ($1, $2 and named groups) in a results list below the highlighted text.

Support for Standard JavaScript Flags

Type the flags you need into the flags box, such as g (global), i (case-insensitive), m (multiline), s (dotAll) and u (unicode); the tool always lists every match, as if g were set.

Why processing in your browser matters

Many online tools upload your files or text to a server to process them. This one does the work on your computer or phone, so your data is not sent to us or stored anywhere else. That lowers the risk when you work with confidential material, although you should still follow your organisation's own rules. Read how this works in our Privacy Policy.

  • No uploads: files are opened and saved on your device, so there is no upload or download wait.
  • No account: nothing to sign up for or install.
  • Free to use: no subscriptions or paywalls.

Frequently Asked Questions

Is my test data uploaded or recorded? +
Which regex flavor does this tool use? +
Can I inspect capture group results separately? +
Does it warn against infinite regex loops or catastrophic backtracking? +
Do I need to sign up or create an account? +
Why are only 100 matches listed? +