Regex Tester
Test regular expressions against sample text.
Regex Tester
Test regular expressions against sample text.
About this regex tester
The regex tester runs a regular expression against sample text and highlights what it matches, so you can build and debug a pattern interactively instead of guessing. Adjust the pattern or the flags and the matches update against your own example data.
It is the fastest way to confirm a pattern does what you intend before dropping it into code — validating an input format, pulling fields out of a string, or filtering lines. Testing against realistic samples, including the cases you expect to fail, catches greedy matches and missed edge cases early.
Common uses
- Build and test a validation pattern, such as for emails or codes, against sample input.
- Check what a regular expression matches before using it in code.
- Debug a pattern that is matching too much or too little.
Helpful tips
- Test against realistic samples, including cases you expect not to match.
- Watch greedy quantifiers; they often match more than intended until you make them lazy.
- Confirm the flags you need, such as case-insensitive or multiline, are turned on.
How to use Regex Tester
- Paste or enter a small code, data, text, URL, or configuration sample before using Regex Tester on a larger task.
- Remove secrets, tokens, private URLs, customer data, and production credentials before testing examples online.
- Run the tool and review the generated code or data for syntax, escaping, formatting, and target-environment compatibility.
- Copy the result into a test file, sandbox, API client, or staging environment before using it in production.
- Use related developer tools when you need to format, encode, decode, minify, inspect, or validate another step.
Frequently asked questions
Which regex syntax does the tester use?
It uses JavaScript regular-expression syntax and flags, which closely matches what you would write in browser and Node.js code.
Why does my pattern match more than expected?
Greedy quantifiers like .* expand as far as possible. Use a lazy version like .*? or a more specific character class to narrow the match.
Is Regex Tester free, and does it work on mobile?
Yes. Regex Tester is free to use on JustBloc with no account or installation, and the page is designed to work on desktop, tablet, and mobile browsers.