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Regex Tester
Write and test regular expressions against any input string – live match highlighting, group capture display, and flag controls, all in your browser.
✓ Free✓ No signup✓ Privacy first✓ Runs in your browser
Regex Tester – ToolPremier
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Test string
Replace (optional)

Real-time regex testing · match highlighting · group capture · replace · flags: g i m s u y

How it works
Convert in three steps

1. Enter your regex pattern

Type your regular expression in the pattern field. Toggle flags (global, case-insensitive, multiline, dotall) as needed.

2. Paste your test string

Add the text you want to test against. Matches highlight in real time as you type - no submit button needed.

3. Review matches and groups

See every match position, capture group value, and index listed below the input. Edit the pattern and watch the results update instantly.

FAQ
Common questions
This tester uses JavaScript’s native RegExp engine (ECMAScript regex). This is the correct flavor for JavaScript and Node.js development. Note that regex syntax differs between languages – Python, PHP PCRE, Go, and Java each have minor differences in syntax and feature support. If you’re writing regex for a non-JS environment, verify that the specific syntax you’re using is supported in your target language.
The main flags are: g (global – find all matches, not just the first), i (case-insensitive – treat uppercase and lowercase as equivalent), m (multiline – ^ and $ match start/end of each line, not just the whole string), and s (dotall – . matches newline characters as well as everything else). Most regex patterns need g enabled to show all matches in a test string.
Special characters in regex (. * + ? ( ) [ ] { } ^ $ | \) must be escaped with a backslash when you want to match them literally. For example, to match a period, write \. instead of . – without the backslash, . matches any character.
The most common causes are: the wrong flag combination (forgetting g for global matches, or m for multiline), differences between JS regex and the regex flavor in your programming language, or string escaping – in code, backslashes in string literals often need to be doubled (\\d instead of \d). Test with the same flags your code uses, and check for escaping differences if you’re copying the pattern from a language with different string literal rules.
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About the Regex Tester
Writing regular expressions without instant feedback is painful – a missing backslash or wrong flag silently breaks the pattern and you don’t find out until runtime. This tester gives you a live feedback loop: write the pattern, see what it matches and what it misses, and fix it immediately. Match highlighting shows you exactly which substrings the pattern captures, and the capture group panel shows each group’s value and index so you can verify that groups are capturing what you expect. It uses JavaScript’s native RegExp engine, which makes it directly applicable to frontend code, Node.js scripts, and any other JS environment.
Benefits
  • Live match highlighting - see matched substrings highlighted in the test string as you type.
  • Capture group breakdown - view each group value and index separately, not just the full match.
  • Flag controls - toggle global, case-insensitive, multiline, and dotall modes instantly.
  • JavaScript RegExp engine - results match what your actual JS code will produce.
Privacy
All regex processing runs client-side in your browser. Your patterns and test strings are never transmitted to any server.