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.
Build and test regular expressions in three steps.
Type or paste a regular expression into the pattern field. Select flags like g (global), i (case-insensitive), or m (multiline) as needed.
Paste the text you want to match against. The tool highlights matches in real time as you type or modify the pattern.
See all matches listed with their positions and any captured groups. Refine your pattern until it captures exactly what you need.
Test patterns like ^[\w.-]+@[\w.-]+\.[a-zA-Z]{2,}$ against a list of emails to verify your validation regex catches edge cases before deploying it.
Write patterns to pull timestamps, IP addresses, or error codes from log lines. Use capturing groups to isolate the exact fields you need for analysis.
Build a regex with capture groups, then construct a replacement string using $1, $2 references. Test the pattern here before running it across your codebase.
Break URLs into protocol, host, port, path, and query string using a single regex. Verify that your pattern handles edge cases like trailing slashes and fragment identifiers.
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).
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.
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.
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.
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.
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.