Regex Tester
Test regular expressions against your text. See matches and positions instantly.
Tool guide
About Regex Tester
A regex tester helps you iterate on regular expressions against sample text before adding them to production code. It is useful for parsing logs, validating formats, extracting IDs, and understanding how flags affect matches.
Start with small sample inputs, test edge cases, and avoid overly broad patterns when user input or large text files are involved.
Common use cases
- Test a pattern before using it in JavaScript.
- Extract IDs, emails, URLs, or log fields from text.
- Compare behavior with global or case-insensitive flags.
- Debug why a pattern matches too much or too little.
Practical tips
- Escape literal special characters such as . + * ? when needed.
- Use anchors like ^ and $ when matching the whole string.
- Be careful with catastrophic backtracking in complex patterns.
Related tools
Frequently asked questions
What is a regex flag?
A flag changes matching behavior, such as global matching, case-insensitive matching, or multiline anchors.
Why does my regex match more than expected?
Greedy quantifiers and missing anchors are common causes. Try narrowing the pattern or using non-greedy quantifiers.
Can regex validate every format perfectly?
Regex is useful for many formats, but complex grammars such as full HTML or programming languages often need a parser.
Is Regex Tester free to use?
Yes. Regex Tester is free to use in your browser with no signup required.
Is my data uploaded when I use Regex Tester?
Most FreeTools utilities process data locally in your browser. Tools that call third-party services, such as IP lookup and advertising, are disclosed in the privacy policy.
What can I use Regex Tester for?
Test and debug regular expressions against your text. See all matches instantly. Free online regex testing tool.