How to Test a Regular Expression Online for Free

Try it now: Regex Tester →

Writing a regular expression that works exactly as intended usually takes a few tries — an easy character or quantifier mistake can silently match too much, too little, or nothing at all. Testing it against real sample text before dropping it into code catches those mistakes immediately.

When you need to test a regex

• Confirming a pattern matches exactly the text you expect, and nothing else
• Debugging why a regex isn't matching in your actual code
• Building a validation pattern (like for emails or phone numbers) before using it
• Understanding what an unfamiliar regex from someone else's code actually matches

How to test a regular expression, step by step

1. Open the Regex Tester.
2. Type or paste your regular expression.
3. Paste sample text to test it against.
4. Matches are highlighted directly in the text as you adjust the pattern.

Tips for writing better regex

• Test against both matching and non-matching examples. A pattern that correctly matches valid input but also matches invalid input isn't actually doing its job.
• Watch out for greedy quantifiers. A pattern like .* often matches far more than intended — testing against real text quickly reveals over-matching.
• Build the pattern incrementally. Start with a simple version, confirm it matches, then add complexity piece by piece rather than writing the whole thing at once.

Common questions

Why does my regex work here but not in my code? Different programming languages sometimes have slightly different regex syntax or flags — double-check the flavor your language expects.

What do the highlighted matches mean? Each highlighted section is a portion of the text your pattern matched — if it's highlighting the wrong (or no) text, the pattern needs adjusting.

Can I test multiple patterns against the same text? Yes — swap out the pattern and re-check the same sample text as many times as needed.

Need to confirm your regex actually works? Test your regex for free →