🔍 Regex Tester
Test regular expressions with live matching, highlights, and capture groups. Runs entirely in your browser.
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What Are Regular Expressions (Regex) and Why Every Developer Needs Them
Regular expressions (regex or regexp) are powerful pattern-matching sequences used to search, validate, extract, and replace text in strings. They're supported in virtually every programming language (JavaScript, Python, Java, PHP, Go, Ruby, C#) and in tools like grep, sed, awk, VS Code search, and database queries.
Essential Regex Syntax Reference
.— Any single character (except newline)\d— Any digit (0–9), equivalent to[0-9]\w— Any word character (letters, digits, underscore)\s— Any whitespace (space, tab, newline)*— Zero or more of the preceding element+— One or more of the preceding element?— Zero or one (optional){n,m}— Between n and m occurrences^/$— Start / end of string (or line withmflag)[abc]— Character class: matches a, b, or c(group)— Capture group for extraction(?:group)— Non-capturing groupa|b— Alternation: matches a or b
Common Regex Patterns for Developers
\d+— Match one or more digits[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}— Email validation pattern^https?://— Match URLs starting with http:// or https://^\d{4}-\d{2}-\d{2}$— ISO date format (YYYY-MM-DD)^(?=.*[A-Z])(?=.*[a-z])(?=.*\d).{8,}$— Password strength (min 8 chars, mixed case + digit)\b\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}\b— IPv4 address pattern
Regex Flags Explained
g(global) — Find all matches, not just the first onei(case-insensitive) — Match regardless of upper/lowercasem(multiline) —^and$match start/end of each line, not just the whole strings(dotAll) —.matches newline characters as well