What regex features are supported?

The tool supports JavaScript regex features including character classes, quantifiers, anchors, groups, alternation, lookahead, and common flags (global, case-insensitive, multiline). Some advanced features like lookbehind may have limited browser support. The tool uses the browser's native JavaScript regex engine.

Can I test regex patterns with different flags?

Yes! You can include flags in the pattern (e.g., /pattern/gim) or use the flags selector. Common flags are: g (global—find all matches), i (case-insensitive), m (multiline—^ and $ match line boundaries). You can combine multiple flags.

How do I escape special characters in regex?

Special regex characters (., *, +, ?, ^, $, [, ], {, }, (, ), |, \) must be escaped with backslash (\) if you want to match them literally. For example, to match a period, use \. instead of .. The tool will show syntax errors if special characters aren't properly escaped.

Can I test regex replacements?

Yes! The tool includes replace functionality. Enter a replacement string and click replace to see how your regex pattern would replace matches. This is useful for testing find-and-replace operations or text transformations.

What's the difference between greedy and non-greedy matching?

Greedy quantifiers (*, +, ?) match as much as possible, while non-greedy (*?, +?, ??) match as little as possible. For example, /.*/ matches the entire string, while /.*?/ matches the shortest possible string. Use non-greedy when you want shorter matches.

What regex flags are supported?

The tool supports all JavaScript regex flags: g (global — match all occurrences), i (case-insensitive), m (multiline — ^ and $ match line boundaries), s (dotAll — . matches newlines), u (unicode — full Unicode support), and y (sticky — match from lastIndex). Flags can be combined for complex matching scenarios.

Can I use named capture groups?

Yes. The tool fully supports named capture groups using the (? ...) syntax. For example, (? \d{4})-(? \d{2})-(? \d{2}) captures date components by name. Named groups are displayed in the match results with their group names, making complex pattern debugging much clearer.

How do I match text across multiple lines?

By default, the . character does not match newlines. To match across multiple lines, enable the 's' (dotAll) flag, which makes . match any character including newlines. Alternatively, use [\s\S] to match any character. For matching at line boundaries, enable the 'm' (multiline) flag to make ^ and $ match the start/end of each line rather than the entire string.

Regex Tester - Test Regular Expressions Free

When to Use This Tool

Use this when:

You're developing code and need to test or debug regular expression patterns
You want to validate regex patterns before using them in your application
You're learning regular expressions and need to test patterns with different text inputs
You need to find all matches of a pattern in text and see highlighted results
You want to test regex flags (global, case-insensitive, multiline) and see their effects
You're working with text processing and need to verify regex patterns work correctly
You need to extract specific patterns from text and want to test the extraction regex

Don't use this if:

You need to process very large texts (over 1 million characters may process slowly)
You want to test regex patterns that require server-side processing or database queries
You need advanced regex features not supported by JavaScript (use specialized regex tools)
You require regex performance testing or benchmarking (use specialized performance tools)
You want to test regex patterns for languages other than JavaScript (regex syntax may differ)

What is a Regex Tester?

A regex tester lets you write, test, and debug regular expressions against sample text with real-time match highlighting, capture group extraction, and flag configuration. Our tool processes everything in your browser — your patterns and test data are never transmitted.

Regular expressions are a powerful but complex tool used in every programming language for text searching, validation, parsing, and transformation. Testing regex patterns interactively, rather than running code repeatedly, dramatically speeds up development and reduces bugs.

This tool is essential for software developers writing validation patterns (email, phone, URL), back-end engineers parsing log files, data engineers building ETL text transformations, DevOps engineers writing configuration rules, and anyone learning regex who wants immediate visual feedback.

Compared to regex101.com (which sends your patterns and test data to their server) or testing in a code editor (which requires running the program), PureXio's tester provides instant, private regex testing with visual match highlighting directly in your browser.

The tool supports JavaScript regex syntax with all flags (global, case-insensitive, multiline, dotAll, unicode), highlights all matches in the test text with distinct colors for different capture groups, shows detailed match information including group names and indices, explains each part of your pattern, and provides a quick reference for common regex syntax.

Best for: testing and debugging regular expressions in real time. Match highlighting, capture groups, flag controls. Supports JavaScript regex. Fully private.

How to Test Regular Expressions

Enter your regex pattern in the pattern field (e.g., /hello|world/g). You can include flags (g, i, m) in the pattern or use the flags selector

Enter test text in the test string field. The tool automatically tests the pattern and highlights matches in real-time as you type

Review matches highlighted in the test text. See match details including match groups, indices, and counts. Use replace functionality to test replacements

Common Use Cases

Test email validation regex pattern (e.g., /^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$/) against sample email addresses

Find all URLs in text using regex pattern (e.g., /https?:\/\/[^\s]+/g) and see highlighted matches

Test phone number extraction regex to find all phone numbers in a document

Validate date format regex patterns (e.g., /\d{4}-\d{2}-\d{2}/) against date strings

Test password strength regex to verify password requirements are met

Extract specific patterns from text (e.g., hashtags, mentions, codes) using regex

Debug complex regex patterns by testing with various input strings

Features

Test regular expressions with live matching and real-time highlighting

Support for all common regex flags: global (g), case-insensitive (i), multiline (m)

Visual highlighting of matches in test text for easy identification

Match details display: shows all matches with indices, groups, and capture groups

Replace functionality: test regex replacements with replacement strings

Real-time validation: see if regex pattern is valid or has syntax errors

100% private—all processing happens in your browser

Limitations & Constraints

Uses JavaScript regex engine—regex syntax and features are limited to JavaScript regex capabilities

Very long texts (>1 million characters) may process slowly or cause browser performance issues

Complex regex patterns with many alternations or nested groups may be slow to process

Some advanced regex features (lookbehind, named groups in older browsers) may have limited support

Regex patterns that cause catastrophic backtracking may hang or crash the browser

Troubleshooting

Regex pattern shows 'Invalid regex pattern' error

Solution: Check regex syntax—common issues include unescaped special characters, unmatched brackets or parentheses, or invalid flag combinations. Ensure special regex characters (., *, +, ?, ^, $, etc.) are properly escaped if you want literal matches. Review regex syntax rules and fix syntax errors. Prevention: Learn regex syntax basics. Test simple patterns first before complex ones.

Regex matches nothing when it should match

Solution: Check if you need the global flag (g) for multiple matches—without it, only the first match is found. Verify the test string actually contains text that matches your pattern. Check case sensitivity—use the case-insensitive flag (i) if needed. Test with simpler patterns first to verify the tool works. Prevention: Test regex patterns incrementally—start simple, then add complexity.

Regex matches too much or matches unexpected text

Solution: Regex patterns are greedy by default—they match as much as possible. Use non-greedy quantifiers (*?, +?, ??) if you need shorter matches. Add word boundaries (\b) if you want whole-word matches. Be more specific with your pattern—narrow the matching criteria. Test with various inputs to refine your pattern. Prevention: Test regex with edge cases to ensure it matches only what you want.

Browser becomes slow or unresponsive when testing regex

Solution: Very long test strings (>100,000 characters) or complex regex patterns may cause performance issues. Catastrophic backtracking in regex patterns can hang the browser. Simplify the regex pattern or reduce test string length. If the browser hangs, refresh the page. Prevention: Test with smaller strings first. Avoid regex patterns that cause catastrophic backtracking.

Capture groups not showing or working incorrectly

Solution: Capture groups are defined with parentheses () in regex. Ensure your pattern has proper group syntax. Groups are shown in match details. If groups aren't capturing, check that parentheses are not escaped. Test with a simple pattern first (e.g., /(\d+)/) to verify groups work. Prevention: Understand regex group syntax. Test group patterns separately before using in complex patterns.