Common Regular Expression Examples and Testing
Test a regular expression against sample text and inspect matches for pattern, group and rule debugging.
What to know before you start
The tester follows JavaScript RegExp behavior. Other regex engines such as PCRE, .NET, Java or Python can support different syntax and semantics.
Recommended workflow
- Write the smallest pattern that expresses the rule, then create examples that should match and should not match.
- Test flags and capture groups separately before combining them into a larger expression.
- Use representative production data and guard against catastrophic backtracking when patterns become complex.
How to check the result
Recheck the result against the original input and the rule you intended to apply. The tester follows JavaScript RegExp behavior. Other regex engines such as PCRE, .NET, Java or Python can support different syntax and semantics.
Common mistakes
Common failures come from wrong units, ambiguous assumptions, changing the rule after seeing a result, or using a quick browser workflow where a regulated or specialist process is required.
Frequently asked questions
Why does a regex work in one language but not here?
Regular-expression engines differ. This tester targets JavaScript RegExp syntax and behavior.
What does the g flag do?
It searches for multiple matches instead of stopping after the first match.
Regex Tester
Test a regular expression against sample text and inspect matches for pattern, group and rule debugging.
Open the related toolRegex Tester
Test a regular expression against sample text and inspect matches for pattern, group and rule debugging.
Open Regex Tester