Regex Tester: What It Does
Tests regular expressions against sample text in real time with capture group inspection, syntax highlighting, and flag toggles (g, i, m, s, u). It breaks down complex patterns into readable syntax tokens.
Example
Pattern: /(\w+)@(\w+\.\w+)/, Text: test@mango.devMatch 1: test@mango.dev, Group 1: test, Group 2: mango.devEvaluates the expression and extracts numbered capture groups.
How to Use
- Enter your regular expression and choose regex flags in the top bar.
- Type or paste test strings into the target editor.
- Inspect match counts, capture group indices, and replacement string previews.
Limitations
- Evaluates using the JavaScript RegExp engine, which differs slightly from PCRE or Python re.
- Catastrophic backtracking patterns can briefly freeze the browser tab.
Frequently Asked Questions
What is the difference between the 'm' (multiline) and 's' (dotAll) regex flags?
The multiline flag (m) makes ^ and $ match line breaks, while dotAll (s) allows the dot (.) token to match newline characters as well.
Does this tester support regex lookbehinds?
Yes. Modern JavaScript engines fully support positive (?<=...) and negative (?<!...) lookbehinds.
Command-Line Equivalent
grep -E 'pattern' file.txtTest extended regular expressions with grep in terminal.
Embed or Cite Regex Tester
Embed this interactive utility directly into documentation or blog posts, or link via GitHub badge:
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