Regex Tester
Test regular expressions online. Enter your regex pattern and test string to see matches highlighted in real-time.
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Regular Expression Quick Reference
Regular expressions (regex) are pattern-matching sequences used for searching, validating, and transforming text. Mastering regex eliminates dozens of conditional string-checking functions with a single, concise pattern.
Essential Regex Syntax
- . — any character; \d — digit [0-9]; \w — word char [a-zA-Z0-9_]
- \s — whitespace; ^ — start of string; $ — end of string
- * — 0 or more; + — 1 or more; ? — 0 or 1; {n,m} — between n and m
- [abc] — character class; [^abc] — negated class
- (group) — capture group; (?:group) — non-capturing group
Common Regex Patterns
- Email:
^[\w.-]+@[\w.-]+\.\w{2,}$ - Phone (US):
\(?\d{3}\)?[-.\s]?\d{3}[-.\s]?\d{4} - Date (YYYY-MM-DD):
\d{4}-(?:0[1-9]|1[0-2])-(?:0[1-9]|[12]\d|3[01]) - IPv4:
\b(?:\d{1,3}\.){3}\d{1,3}\b
What is the difference between greedy and lazy matching?
Greedy quantifiers (* + {}) match as many characters as possible. Lazy quantifiers (*? +? {}?) match as few as possible. Example: in "ab>cd>ef", the pattern <.*> (greedy) matches the entire string; <.*?> (lazy) matches only the shortest possible match. Use lazy matching when extracting specific delimited content.
Are regex patterns the same across languages?
Core syntax is mostly compatible, but flavor differences exist. JavaScript uses /pattern/flags syntax. Python's re module uses PCRE-like syntax. Always test regex in the specific language environment you'll deploy in — this tester uses JavaScript's regex engine.