Regex Tester
Test regular expressions against sample input. Free online developer tool for fast browser-based work.
What is this tool?
Regex Tester lets you try a regular expression against sample text before it reaches code, validation logic or QA cases. It is useful for spotting escaping issues and unexpected matches.
How to use
- Enter a regular expression and a representative sample string.
- Check whether the highlighted matches align with the rule you intended.
- Adjust flags, anchors and character classes before copying the pattern into code.
Practical example
Test positive and negative samples before using a regular expression in production.
Pattern:
^[^\s@]+@[^\s@]+\.[^\s@]+$
Test text:
contact@example.com
Result:
1 match found.API
Regex workflows are usually interactive, but API docs can help pair patterns with repeatable text fixtures and validation examples.
When to use
Related tools
Privacy
Use test strings or reduced examples. Avoid pasting logs that contain tokens, IP-linked personal data, credentials or private customer text.
Frequently asked questions
Why does my regex match too much?
Greedy quantifiers, missing anchors or broad character classes often capture more text than intended.
Should I validate complex formats only with regex?
Regex is useful for shape checks, but complex domain rules often need application logic too.
What examples should I test?
Use both accepted and rejected samples so you can see false positives and false negatives.
Limitations / when not to use
A pattern that works on a small sample may still fail on real-world edge cases. Keep a set of positive and negative examples with the regex.