Test Regex Online — Free Real-Time Regex Tester

Why Use an Online Regex Tester?

Regular expressions are one of the most powerful tools in a developer's toolkit, but writing them correctly can be challenging. A single misplaced character or forgotten escape sequence can cause your pattern to match nothing — or worse, match the wrong things. An online regex tester eliminates the guesswork by showing you exactly what your pattern matches in real time.

Instead of running your code, feeding in test data, and checking logs, you can paste your regex and test string into a browser-based tool and see results instantly. This tight feedback loop dramatically speeds up pattern development and debugging. Whether you're validating user input, parsing log files, or extracting data from text, a regex tester helps you iterate faster and catch errors before they reach production.

Regex Shuttle's online tester goes beyond simple matching. It highlights every match in your test string, shows you the exact index positions, displays all capture groups with their values, and even lets you test substitution patterns. All processing happens locally in your browser — your data never leaves your device.

Key Features of the Regex Shuttle Tester

How to Test a Regular Expression Online

1. 1

   Enter your regex pattern

   Type or paste your regular expression into the pattern input field. You can use any valid JavaScript regex syntax including character classes, quantifiers, anchors, and groups.

2. 2

   Set your flags

   Toggle regex flags using the checkboxes: g for global matching (find all matches), i for case-insensitive matching, m for multiline mode, s for dotAll (dot matches newlines), and u for Unicode support.

3. 3

   Add your test string

   Paste or type the text you want to test against your regex. This can be any string — log entries, user input, CSV data, HTML, or any other text.

4. 4

   Review the matches

   See all matches highlighted in your test string. Each match shows its full text, start index, length, and any captured groups.

5. 5

   Test substitution (optional)

   Enter a replacement pattern in the substitution field to preview find-and-replace results. Use $1, $2, etc. to reference capture groups.

Common Regex Patterns to Test

Here are some frequently used regular expressions you can test right now. Click any pattern to load it into the tester above:

Understanding Regex Flags

Regex flags modify how a pattern is interpreted and matched. The right flag combination is essential for getting the results you expect. Here's what each flag does:

• g (Global): Finds all matches instead of stopping at the first one. Essential when you need to process every occurrence in your text.
• i (Case-Insensitive): Makes your pattern match both uppercase and lowercase letters. "hello" would also match "Hello", "HELLO", etc.
• m (Multiline): Changes ^ and $ to match the start and end of each line instead of the entire string. Useful for multi-line text processing.
• s (DotAll): Makes the dot (.) character match newline characters as well. Without this flag, dot stops at line breaks.
• u (Unicode): Enables full Unicode matching support. Required for Unicode property escapes and proper handling of surrogate pairs.

Why Regex Shuttle is the Best Online Regex Tester

Unlike other online regex testers that require account creation, display ads, or upload your data to external servers, Regex Shuttle processes everything locally in your browser. Your patterns and test strings never leave your device, making it safe to test sensitive data like log entries, user credentials, or proprietary text.

The tester uses JavaScript's native RegExp engine, which means the results you see are exactly what you'll get in your Node.js or browser code. No surprises, no differences between the tester and your production environment.

With features like real-time matching, capture group visualization, substitution preview, and a built-in pattern library, Regex Shuttle provides everything you need to write, test, and debug regular expressions — all for free, with no sign-up required.