Regex tester
Test regular expressions with real-time match highlighting, group capture display, and flag toggles
Regex Tester
Test regular expressions with live highlighting
TL;DR
What is Regex tester?
A regular expression (regex) is a sequence of characters that defines a search pattern. Regex engines use this pattern to find, match, extract, or replace substrings within text. They are supported natively in JavaScript, Python, Java, Go, and virtually every other programming language.
Common use cases
- ‣Input validation: check that an email address, phone number, or postal code matches a required format
- ‣Log parsing: extract structured fields (timestamps, IP addresses, error codes) from unstructured log lines
- ‣Search and replace: rename variables, reformat dates, or transform text across an entire codebase in one pass
- ‣String splitting: divide a string by complex or variable-length delimiters that a simple split cannot handle
Frequently asked questions
What do the flags g, i, and m mean?
g (global) finds all matches instead of stopping at the first. i (case-insensitive) treats uppercase and lowercase letters as equal. m (multiline) makes ^ and $ match the start and end of each line rather than the entire string.
Why does my regex match too much?
This is usually caused by greedy quantifiers. .* matches as many characters as possible. Use .*? (lazy) to match as few characters as possible, or replace . with a more specific character class such as [^\n] to avoid matching across line breaks.
Is JavaScript regex the same as Python regex?
They share most syntax but differ in some features. JavaScript does not support atomic groups or possessive quantifiers. Python's re module uses (?P<name>) for named groups while JavaScript uses (?<name>). Always test in the language you plan to deploy in.
See also
- ‣Text diff: diff text before and after a global regex replacement to verify the substitution changed only what was intended
- ‣String obfuscator: use regex to identify and locate sensitive patterns in text, then obfuscate matched regions