Use the free QuickToolz developer tools — no signup, no install, works in your browser.
How to Use Regex Tester
Step 1
Enter your pattern
Step 2
Paste test string
Step 3
View matches
Step 4
Refine pattern
What Is a Regex Tester?
A regex tester is an online tool that lets you write, test, and debug regular expressions in real time. You enter a pattern and a test string, and the tool instantly highlights all matches, shows capture groups, and reports errors in your pattern. It eliminates the need to run code just to test a regex.
How to Test a Regular Expression Online
- Enter your regex pattern in the pattern field (without delimiters).
- Paste your test string — the text you want to match against.
- View matches highlighted in real time as you type.
- Refine your pattern until it matches exactly what you need.
Regex Flags Explained
g (global): Finds all matches in the string, not just the first one.
i (case-insensitive): Makes the match ignore uppercase vs lowercase differences.
m (multiline): Makes ^ and $ match the start and end of each line, not just the whole string.
s (dotAll): Makes the dot (.) match newline characters as well as other characters.
Common Regex Patterns
Email address: [a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}
Phone number (US): \(?\d{3}\)?[-.\s]?\d{3}[-.\s]?\d{4}
URL: https?:\/\/(www\.)?[-a-zA-Z0-9@:%._\+~#=]{1,256}\.[a-zA-Z0-9()]{1,6}
IP address: \b\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}\b
Date (YYYY-MM-DD): \d{4}-\d{2}-\d{2}
Tips for Writing Better Regex
Be as specific as possible — overly broad patterns cause false matches. Use anchors (^ and $) when you need to match the entire string. Use non-greedy quantifiers (*? and +?) when you need the shortest possible match. Test against edge cases including empty strings, very long inputs, and unusual characters.
Frequently Asked Questions
Which regex flavor does the tester use? QuickToolz uses JavaScript regex, which is compatible with most modern web applications.
Can I test capture groups? Yes — the tool shows each capture group separately so you can verify what each group matches.