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Regex generator
Describe what you want to match in plain English. Get the regex pattern, an explanation of each part, alternative approaches, and live test results against your own strings.
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Frequently asked questions
How specific should my description be for the best regex output?
The more specific, the better. Instead of 'match an email address', try 'match an email address where the local part can contain letters, numbers, dots, plus signs, and hyphens, and the domain must have at least one dot'. Mentioning edge cases you want to handle or exclude — like whether to allow subdomains or international characters — significantly improves the result.
What do the case insensitive and multiline flags do?
The case insensitive flag (i) makes the pattern match both upper and lowercase letters without needing to specify each. For example, /hello/i matches Hello, HELLO, and hello. The multiline flag (m) changes how the anchors ^ and $ behave — instead of matching the start and end of the entire string, they match the start and end of each line. This is important for patterns that need to match across line breaks.
Why does my generated regex match more than I expected?
This is usually caused by missing anchors. Without ^ at the start and $ at the end, a regex matches anywhere within the string — so a pattern meant to validate a full phone number might also match the digits within a longer string. The generator adds anchors when appropriate, but always test your regex with strings that should not match to verify boundaries.
Can I use the generated regex in any programming language?
Most of the generated patterns use standard regex syntax that works across JavaScript, Python, PHP, Ruby, and Java. Language-specific features (like Python's named capture groups syntax or Java's possessive quantifiers) are avoided by default. Check the generated explanation — if it mentions a specific feature, verify it is supported in your target language.
Writing regex that actually works
Regular expressions are powerful but easy to get wrong. Small mistakes — a missing anchor, an unescaped dot, or a greedy quantifier — can cause subtle bugs that only appear with specific inputs.
Always test with edge cases. A regex that matches valid email addresses should also be tested against: strings with multiple @ signs, addresses with plus addressing (user+label@domain.com), internationalized domains, and empty strings.
Anchors matter. Without ^ and $, a pattern may match as a substring when you expected a full-string match.
Beware of catastrophic backtracking. Patterns with nested quantifiers like (a+)+ can cause exponential time complexity on certain inputs. Always test with adversarial strings before using regex in production validation.
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