How to Test a Regex Pattern
- Don't know regex? Scroll to the pattern library and click a preset like “IPv4 Address” or “Email Address” — the pattern, flags, and a demo test string fill in automatically.
- Know what you're looking for? Type or paste your own pattern into the field at the top, then paste your own sample text into the left panel.
- Read the results. Matches highlight instantly on the right, with a full list below showing each match and any capture groups — click Copy on any one.
What Is a Regular Expression?
A regular expression (regex) is a small pattern language for describing the shape of text — “a run of digits,” “anything between two quotes,” “a word followed by an @ and a domain” — rather than an exact string. That makes it useful for searching, validating, and extracting data from things like log files, form input, and CSV columns without writing custom parsing code for each case. The tradeoff is that regex syntax is dense and easy to get subtly wrong, which is exactly what this tool's live highlighting and ready-made pattern library are for — see the results immediately instead of guessing.
Frequently Asked Questions
What is a regex tester?
A regex tester lets you try out a regular expression pattern against sample text and see exactly what it matches, without writing code — useful for building or debugging a pattern before using it in a script, a log search, or a form validator.
Do I need to know regex to use this?
No. The pattern library covers common needs — IP addresses, timestamps, log levels, emails, URLs, UUIDs, and more — with a hand-written plain-English explanation for each. Click one to insert it and see it work immediately.
Is my test data uploaded anywhere?
No. Your pattern and test text are processed entirely in your browser using JavaScript's built-in regex engine — nothing is ever sent to a server.
What do the Multiline and Dot matches newline flags do?
Multiline makes ^ and $ match the start and end of each line instead of only the start and end of the whole text — useful when testing against multi-line log dumps. Dot matches newline makes the . wildcard also match line breaks, which it doesn't by default.