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Regex Tester

Test regular expressions with real-time match highlighting, capture groups, and replace mode.

Uses JavaScript regex syntax. Your data stays in your browser.

or try sample data

What is a Regular Expression?

A regular expression (regex) is a pattern that describes a set of strings. Regexes are used for searching, matching, and replacing text in virtually every programming language. This tester uses JavaScript's native RegExp engine so your patterns will behave exactly as they would in browser or Node.js code.

  • Real-time matching — see matches highlighted as you type the pattern.
  • Capture groups — view individual group captures for each match.
  • Replace mode — test string replacement with back-references ($1, $2, etc.).
  • All flags — global, case-insensitive, multiline, and dotAll.
  • Privacy-first — all pattern matching runs in your browser.

Frequently Asked Questions

How do I test a regular expression online?

Enter your regex pattern in the pattern field and your test string in the input area. The tool instantly highlights all matches in real time as you type. You can also set flags like case-insensitive (i), global (g), and multiline (m).

What is a regular expression (regex)?

A regular expression is a sequence of characters that defines a search pattern. Regex is used in programming for text searching, validation, extraction, and replacement — for example, validating email addresses, extracting phone numbers, or finding patterns in log files.

Is my test data private when using this regex tester?

Yes. All pattern matching runs entirely in your browser using JavaScript's built-in RegExp engine. No data or patterns are sent to any server, so it's safe to test regex against sensitive text like log files, credentials, or private data.

What regex flags are available?

This tool supports standard JavaScript regex flags: g (global — find all matches), i (case-insensitive), m (multiline — ^ and $ match line boundaries), s (dotAll — dot matches newlines), and u (Unicode). Combine flags to customize matching behavior.

Can I use this tool for regex find-and-replace?

Yes. Enter a replacement pattern in the Replace field to preview substitutions. The tool supports back-references ($1, $2, etc.) for capturing groups, so you can rearrange, transform, or reformat matched text.

How is this different from regex101?

Both tools test regex patterns in real time. This tool is focused on simplicity and privacy — it runs entirely client-side with no account needed. It's ideal for quick tests. For advanced features like regex debugging, explanation, and community pattern libraries, regex101 offers more depth.