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Regex Checker Tool

Test regular expressions in real-time with match highlighting, explanations, and a pattern library.

Last updated: 2026/10/16 Developer Feedback & bug reports
Regular Expression
/ /
Test String
Match Result
Enter a test string to see matches
Replace
Replace Preview
Explanation

    Common Regex Patterns

    Regex Cheat Sheet

    Click any item to insert it at the cursor position in the regex field. Covers metacharacters, quantifiers, groups, lookarounds, and more.

    How to Use

    1

    Enter Regex

    Enter a regular expression pattern. Toggle flags (g, i, m, s, u) as needed.

    2

    Enter Test String

    Enter a test string to see matches highlighted in real-time.

    3

    View Results

    Check the match details table for group captures and positions. Use the Replace tab to preview replacements.

    4

    Use Pattern Library

    Insert common regex patterns with one click from the pattern library.

    About Regex Checker

    A web tool to test regular expressions in real-time using JavaScript's regex engine. All processing happens in your browser. Your text is never sent to any server.

    Features

    • Real-time MatchingSee matches highlighted instantly as you type. Debug regex efficiently.
    • Explanation PanelEach token is explained clearly. Great for learning regex.
    • Pattern Library (25+)Insert common patterns for email, phone, URL, date, and more with one click.
    • Privacy ProtectedAll processing happens in your browser. Text is never sent to servers.

    Use Cases

    • Test input validation regex (email, phone, postal code)
    • Test log file pattern extraction
    • Verify Google Analytics filter patterns
    • Create search & replace patterns for text editors
    • Learn and understand regex syntax

    Related Tools & Guides

    To bulk-rewrite text you matched or extracted with regex, try the Text Replace tool; to sort lines or remove duplicates, use the Text Sort & Dedupe tool. To pull values out of JSON, pair it with the JSONPath Tester tool. To learn the basics, see our Regex Introduction guide, and for everyday patterns, the Common Regex Patterns guide.

    FAQ

    Is the regex checker free to use?
    Yes, completely free. No registration required.
    Which regex engine is used?
    It uses JavaScript's regex engine (ECMAScript). Some syntax may differ from PHP (PCRE) or Python (re).
    Is my text saved anywhere?
    No, your text is never sent to or stored on any server. All processing is local.
    Can I test regex with Japanese text?
    Yes, Japanese text is fully supported. Enable the Unicode flag (u) for proper surrogate pair handling.
    Can I use the patterns from the library in my code?
    The patterns are common examples. Adjust them to your specific requirements.
    Why does my regex show "No match"?
    Common causes: 1) Missing flags (use i for case-insensitive), 2) Anchor misuse (^ and $ without m flag), 3) Missing escapes for special characters.
    How do $1 and $2 work in replacement?
    $1 refers to the 1st capture group, $2 to the 2nd, etc. Named groups use $<name>.
    Can I use it on my smartphone?
    Yes, it works on all devices including smartphones, tablets, and PCs.
    How does this compare to regex101?
    regex101 supports multiple engines for advanced users. This tool focuses on usability with an explanation panel and pattern library.
    What are the differences between JavaScript and PHP regex?
    Key differences: 1) PHP PCRE supports recursive patterns and atomic groups, JS does not. 2) Lookbehind support varies. 3) Named capture syntax differs slightly.
    Where can I see match highlighting and capture groups?
    When you enter a test string, matches are highlighted in two alternating colors in the "Match Result" area. The "Match Details" table also lists each match position (start-end) and the contents of capture groups (()) and named groups ((?<name>)).
    Can I preview replacements and toggle flags?
    Yes. Toggle flags (g/i/m/s/u) with one click using the buttons next to the input. Open the "Replace" section and enter a replacement string ($1, $2 reference groups) to see a real-time preview with deleted and inserted parts color-coded, then copy the result.

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    Related Guides

    Regular Expressions for Beginners: Metacharacters and How to Write Regex Learn how to write regular expressions from scratch: the core metacharacters . * + ? [] () | ^ $, quantifiers, common patterns for email, phone, and URLs, groups and replacement, and tips for learning regex. Common Regex Patterns: Email, Phone, URL, ZIP, Date Examples and Pitfalls Practical regular expression patterns for everyday use, with examples for email, phone number, URL, postal code, date, and full-width/half-width text. Covers metacharacters, quantifiers, and groups, plus why you should not over-trust regex.