Test regex patterns with live matching
Test and debug regular expressions online with real-time matching. Highlight matches, view groups, and test regex patterns. Free regex tester tool.
Enter your regular expression pattern in the pattern input field. The tool supports the full JavaScript regex syntax including character classes, quantifiers, anchors, groups, lookaheads, and lookbehinds.
Set the regex flags: g (global - find all matches), i (case insensitive), m (multiline - ^ and $ match line boundaries), s (dotAll - dot matches newlines), and u (Unicode support).
Paste or type the test string you want to match against in the text area below. The tool highlights all matches in real time as you type both the pattern and the test string.
Review the match results showing each match, its position in the string, and any captured groups. This detailed output helps you verify and debug complex patterns.
Building and debugging regular expressions is one of the most common challenges developers face. This tool provides instant visual feedback showing exactly what your pattern matches, where it matches, and what groups it captures, dramatically reducing the trial-and-error debugging cycle.
The real-time highlighting makes it easy to see unintended matches or missed text. When your pattern captures too much or too little, the visual feedback immediately shows the problem, making regex development significantly faster.
Whether you are validating email addresses, parsing log files, extracting data from text, performing search-and-replace operations, or building input validation rules, this tool lets you test and perfect your patterns before implementing them in your code.
All regex testing runs locally in your browser. Test strings containing sensitive data like log files, user data, or configuration content remain completely private.
The tool helps developers learn regex by showing the immediate effect of each pattern change. The visual match highlighting makes abstract regex concepts tangible and understandable.
Start with a simple pattern and gradually add complexity. Test each addition to verify it matches correctly before adding the next element.
Use non-capturing groups (?:...) when you need to group parts of a pattern but do not need the matched text in the results. This improves performance and keeps your captures clean.
Be cautious with greedy quantifiers (*, +) which match as much text as possible. Use lazy quantifiers (*?, +?) when you want to match as little text as possible.
For complex patterns, add comments using the verbose mode pattern or break the regex into named groups (?<name>...) for self-documenting code.
Always test your regex with edge cases: empty strings, special characters, very long text, and boundary conditions to ensure robust behavior.
A regular expression (regex) is a sequence of characters that defines a search pattern used for matching, finding, and manipulating text. Regex is used in virtually every programming language and many text editors for tasks like input validation (email, phone numbers), search and replace operations, data extraction from text, log file parsing, and text formatting. Learning regex is an essential skill for developers, data analysts, and system administrators.
The most common flag is 'g' (global) which finds all matches instead of stopping at the first one. Use 'i' (case insensitive) when you want to match regardless of letter case. Use 'm' (multiline) when you want ^ and $ to match the start and end of each line rather than the entire string. The 's' (dotAll) flag makes the dot character match newlines. Use 'u' (Unicode) for proper handling of Unicode characters and emoji.
A practical email regex pattern is: ^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$. This matches most standard email formats. However, the official email specification (RFC 5322) allows many unusual formats that are extremely difficult to capture with regex. For production use, it is better to use a simple pattern for basic validation and then verify the email by sending a confirmation message.
Greedy quantifiers (*, +, ?) match as much text as possible while still allowing the overall pattern to succeed. Lazy quantifiers (*?, +?, ??) match as little text as possible. For example, with the text '<b>hello</b><b>world</b>', the greedy pattern '<b>.*</b>' matches everything from the first <b> to the last </b>, while the lazy pattern '<b>.*?</b>' matches each <b>...</b> pair individually.
This tool uses JavaScript's regex engine, which shares most syntax with other languages including Python, Java, C#, PHP, and Ruby. Core features like character classes ([a-z]), quantifiers (*, +, ?), anchors (^, $), and groups work identically across languages. Some advanced features like lookbehinds, possessive quantifiers, and recursive patterns may differ between language implementations.
Yes, completely private. All regex matching happens in your browser using JavaScript's built-in RegExp engine. Your test strings and patterns are never sent to any server, never stored, and never logged. This makes the tool safe for testing patterns against log files, user data, configuration files, and any other sensitive text.
Capturing groups are created by wrapping part of your pattern in parentheses. For example, (\d{3})-(\d{4}) matches a phone format and captures the two number groups separately. Named groups use (?<name>...) syntax for clarity. Access captured groups by their index (group 1, 2, etc.) or by name in your code. Non-capturing groups (?:...) group without capturing when you need grouping but not the matched text.