What is a Regex Tester?
A regex tester lets you write a regular expression pattern and instantly see which parts of a test string it matches. It highlights matches in context and shows captured groups, making it much faster to debug a pattern than testing it inside actual application code.
How to Use This Regex Tester
- Type your pattern into the Pattern field (without surrounding slashes).
- Check the flags you need — g, i, m, or s.
- Paste your test string into the Test String box.
- Matches highlight automatically as you type, with a live match count and capture group breakdown.
When Do You Need a Regex Tester?
Use a regex tester when validating form inputs like emails or phone numbers, extracting structured data from logs or text files, building find-and-replace patterns for code refactors, or simply debugging why a pattern that looked correct isn't matching what you expect. Seeing live highlighted matches makes pattern mistakes obvious immediately.
Frequently Asked Questions
What is a regular expression?
A regular expression (regex) is a sequence of characters that defines a search pattern, used to match, extract, or replace text based on rules rather than exact strings.
Regex flags explained?
g (global) finds all matches instead of stopping at the first. i (case insensitive) ignores letter casing. m (multiline) makes ^ and $ match the start and end of each line. s (dotAll) lets . match newline characters too.
How to match email with regex?
A common pattern is ^[^\s@]+@[^\s@]+\.[^\s@]+$ — it requires characters before an @, characters after it, a literal dot, and a domain suffix, while disallowing whitespace and extra @ symbols.
Regex greedy vs lazy?
Greedy quantifiers like * and + match as much text as possible by default. Adding a ? after them (*? or +?) makes them lazy, matching as little text as possible while still satisfying the pattern.