RegEx Tools
RegEx Tools
Test regular expressions against any input with live match highlighting; see capture groups, match indices, match count, and replacement output as you type. Visualize patterns as railroad diagrams, get token-by-token explanations, check for catastrophic-backtracking (ReDoS) risk, and browse a curated pattern library.
RegEx Tools
Test regular expressions against any input with live match highlighting; see capture groups, match indices, match count, and replacement output as you type. Visualize patterns as railroad diagrams, get token-by-token explanations, check for catastrophic-backtracking (ReDoS) risk, and browse a curated pattern library.
Common uses
- Test an email validation regex against sample input
- Extract all URLs from a text block
- Use named capture groups for date parsing
- Check a pattern for catastrophic-backtracking risk
Also searched as
- regex tester online
- regex101 alternative
- explain regex pattern
- regex railroad diagram visualizer
- check regex for catastrophic backtracking
- redos checker
- regex named capture groups tester
- regex find and replace online
- common regex patterns library
- regex for email validation
- regex lookahead lookbehind tester
- regex match highlight capture groups
Frequently asked questions
How do I test a regular expression?
Enter your pattern and flags, then type a test string. Matches and capture groups are highlighted live as you type.
Does it explain what a regex does?
Yes. The tool breaks a pattern down token by token and includes a searchable library of common ready-made patterns.
How do I test a regular expression online?
Enter your pattern and sample text and matches are highlighted as you type, with capture groups, named groups and the replacement output.
How can I check if a regex is vulnerable to ReDoS?
The tool checks a pattern for catastrophic-backtracking risk, such as nested quantifiers, and warns you if it looks risky. Treat it as a heuristic and test with real inputs too.
Can it explain what a regex does?
Yes, it gives a token-by-token explanation and can draw the pattern as a railroad diagram.
Is there a library of common regex patterns?
Yes, there is a curated pattern library with ready-made patterns such as email, URL, IP and phone number.
Does it support named groups and replacement?
Yes, you can use named capture groups and see the substitution output live.
Is my data uploaded to a server?
No. This tool runs entirely in your browser — your input is processed locally on your device and is never uploaded or stored on a server.