What is this tool?
The Regex Tester lets you try a JavaScript regular expression against sample text. It shows matches, groups, and flags so you can understand what the pattern is doing.
It is useful before adding regex to validation, search, parsing, log checks, import scripts, or frontend forms.
Why use this tool?
- It gives quick feedback while you build a pattern.
- It helps catch patterns that match too much or too little.
- It supports common JavaScript flags such as global, ignore case, multiline, dot all, and unicode.
- It makes capture groups easier to inspect.
- It reduces risky copy-paste changes in production code.
How to use it
- 1
Open the Regex Tester.
- 2
Enter your regular expression pattern.
- 3
Select the flags you need, such as global or ignore case.
- 4
Paste realistic test text into the test string box.
- 5
Review matches and capture groups.
- 6
Adjust the pattern until it matches exactly what you expect.
Common use cases
- A developer tests an email-like pattern before adding form validation.
- A backend engineer checks log lines for transaction IDs.
- A data entry team validates invoice codes before import.
- A QA tester confirms a search pattern works with Khmer and English text.
- A student learns how capture groups change regex output.
Tips and best practices
- Use real sample data, including edge cases and bad input.
- Start simple, then add stricter rules.
- Be careful with greedy patterns that match too much text.
- Use anchors when you need the entire input to match.
- Do not rely only on regex for security-sensitive validation.
FAQ
Which regex flavor does the tool use?
It is designed around JavaScript regular expressions, so behavior should match browser JavaScript.
What does the global flag do?
The global flag finds all matches instead of stopping after the first match.
Can regex validate emails perfectly?
Regex can catch obvious format issues, but full email validation is more complex than one simple pattern.
Why does my regex match too much?
The pattern may be greedy or missing anchors. Test with smaller examples and tighten the expression.
Can I copy matches?
Yes. The tool includes copy support for matched output.