RegEx Tester

Test regular expressions live, highlight matches and preview replacements.

/ / {{ flagString }}
{{ regexError }}
{{ matchCount }} {{ matchCount === 1 ? __t('match_singular') : __t('match_plural') }} 
{{ replaceResult }}
# Match Index Groups
{{ i + 1 }} {{ m.value }} {{ m.index }} — ${{ gi + 1 }}: {{ g ?? 'undefined' }}
{{ section.title }}
{{ item.token }} {{ item.desc }}

What Are Regular Expressions?

Regular expressions (RegEx) are powerful search patterns used in text processing and programming. They allow you to define complex string patterns to search, validate, extract or replace text. Almost every programming language — from JavaScript to Python to PHP — supports regular expressions.

Common Use Cases

RegEx is used for email validation, phone number detection, URL parsing, log analysis, data extraction from HTML, search-and-replace in code editors and much more. Our online RegEx tester uses the JavaScript RegExp engine, so you can test patterns directly in your browser.

Tips for Regular Expressions

  • Start with simple patterns and expand step by step — this helps with debugging.
  • Use non-greedy quantifiers (*?, +?) when you need the shortest match.
  • Use capture groups () to extract parts of a match and use them in replacements.
  • Mind the performance: nested quantifiers like (a+)+ can cause catastrophic backtracking.