You are responsible for key management and output validation.
Regex Tester
Test regular expressions live in your browser. See every match with groups and indices, with support for common flags. Zero-knowledge, client-side only.
Matches
0 matchesNo matches found. Check the pattern or try different flags.
How to Test a Regular Expression Online
Learn how to test regular expressions locally in your browser with live match results, flags, and group information.
- 1
Enter your pattern
Type or paste the regular expression you want to test.
- 2
Select flags
Toggle flags such as global, case-insensitive, multiline, dotall, or Unicode.
- 3
Paste test text
Add the text to match against. Results update as you type.
- 4
Review matches
Inspect each match, its index, and captured groups, then copy any value you need.
Common Use Cases
- 1Debug regex patterns before using them in code or CI pipelines
- 2Validate user input formats such as email, phone, or identifiers
- 3Extract data from logs, configs, or test fixtures without uploading them
- 4Build and verify regex for search, scraping, or transformation scripts
Security Tips
- Never paste secrets into online regex tools — many log your input
- Test regex locally so sensitive logs and configuration stay on your device
- Avoid catastrophic backtracking patterns like (a+)+ on untrusted input
- Validate regex in tests with known edge cases, not just happy paths
Frequently Asked Questions
Which regex flavors are supported?
The tester uses JavaScript's native RegExp engine, the same flavor used by Node.js and modern browsers. Quantifiers, groups, lookarounds, and Unicode properties behave as they do in JavaScript.
Are my pattern and test text uploaded?
No. Matching runs entirely in your browser with the native RegExp engine. Nothing is sent to a server, so you can safely test patterns against sensitive logs or configuration.
How do I avoid regex performance problems?
Keep patterns linear where possible and avoid nested quantifiers like (a+)+ which can cause catastrophic backtracking on certain inputs. Test against realistic input sizes before deploying.