How to use Regex Tester
- Enter a regular expression.
- Paste sample text to test against.
- Review highlighted matches and adjust flags/pattern as needed.
Worked examples
Concrete numbers and cases you can check against the tool above.
US ZIP code pattern
^\d{5}(-\d{4})?$ matches 94107 and 94107-1234 but not 9410 or 941070. Test against a few real lines, including a failure case. If you forget ^ and $, the pattern can match a 5-digit street number inside a longer string.
When to use Regex Tester
Regular expressions are easy to get subtly wrong. Live match highlighting shortens the loop versus redeploying code just to test a pattern.
Common use cases
- Validate an email or slug pattern before shipping.
- Debug a log-parsing expression against sample lines.
- Teach students how capture groups behave.
- Prototype find-and-replace patterns for a cleanup script.
Inputs and outputs
- JavaScript-style regular expressions and plain text samples
Privacy
This tool runs entirely in your browser. Your data never leaves your device — nothing is uploaded to our servers.
Frequently asked questions
- Which regex flavor is this?
- It follows JavaScript regular expression behavior in your browser.
- Can I test flags like global or case-insensitive?
- Yes, when flags are exposed in the UI (for example g, i, m).
- Is my text sent to a server?
- No. Testing is local.