What is a JavaScript Regex Tester?
A regular expression (regex) is a powerful pattern language for finding, validating, extracting, or replacing specific patterns in strings. JavaScript regex is widely used for email validation, phone number formatting, Korean (Hangul) text processing, URL parsing, and many other real-world tasks.
This free online regex tester lets you instantly verify JavaScript regular expressions in your browser. Simply type your pattern, set flags (g, i, m, s, u), and see real-time match highlights, capture groups, and replace results — no install or login required. Handy presets for email, phone, Korean characters, and more are included.
Key Features
Real-time Matching
Enter your regex and test string to instantly see highlighted matching results.
Capture Group Analysis
View detailed capture groups, index positions, and matched values for each match.
Replace Functionality
Instantly see the result of replacing matched patterns with your desired string.
Preset Patterns
Apply commonly used regex patterns for email, phone, URL, IP, Korean characters with one click.
How to Use
- Enter Regex — Type your regular expression pattern in the input field at the top.
- Set Flags — Enable flags like g (global), i (case-insensitive), m (multiline), s (dotAll), u (unicode) as needed.
- Enter Test String — Type the string you want to test against and see real-time matching results.
- Check Results — Review match highlights, capture group details, and replacement results.
Use Cases
Email & Phone Regex Validation
Test email regex patterns like [a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,} or phone patterns against real input to build reliable form validators.
Korean (Hangul) Regex Processing
Use [가-힣]+ to match Korean characters exclusively, or combine with \s and punctuation for full Korean text validation — useful for localized apps.
JavaScript Regex Debugging
Copy a regex from your JS/TS code, paste it here, and instantly see why it matches or fails — no need to run your app each time.
Log & Data Cleaning
Extract timestamps, IP addresses, or error codes from server logs, or strip unwanted characters from CSV data using find-and-replace with capture groups.
FAQ
What is a regular expression?
A regular expression (regex) is a formal language for defining and searching patterns in strings. It is supported by most programming languages and text editors, and is used for data validation, extraction, and replacement.
What are flags and what types are available?
Flags modify how a regex behaves. Common flags include g (global search), i (case-insensitive), m (multiline mode), s (dotAll - dot matches newline), and u (unicode support).
What are capture groups?
Capture groups are parts of a regex enclosed in parentheses (). They allow you to extract specific portions of matched strings and reference them as $1, $2, etc. during replacement.
Is this tool free?
Yes, it is completely free with no registration or installation required. Your input data is never sent to any server.
Does this tool support Korean (Hangul) regex patterns?
Yes, full Unicode and Korean regex is supported. Use [가-힣] to match Korean characters, [ㄱ-ㅎ] for consonants, or [ㅏ-ㅣ] for vowels. Enable the u (unicode) flag when working with emoji or supplementary characters. A 'Korean Characters' preset is built in for quick access.
Privacy Notice
This regex tester performs all processing in your browser. Your regular expressions and test strings are never sent to any server. You can safely test sensitive data.
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