Regular expressions are one of the most powerful tools in a developer's toolkit — and one of the easiest to get wrong. A regex tester lets you build and debug patterns interactively, seeing exactly what matches as you type. Our free online regex tester highlights matches live and runs entirely in your browser.
What Is a Regular Expression?
A regular expression (regex) is a pattern used to match character combinations in text. Instead of searching for an exact word, you describe the shape of what you are looking for — "any sequence of digits", "an email address", "a word that starts with a capital letter". Regex is supported in virtually every programming language and many text editors.
How to Test a Regex Online
- Enter your regular expression in the pattern field.
- Paste the text you want to test it against.
- See matches highlighted instantly as you refine the pattern.
- Inspect capture groups to see the specific pieces each match extracts.
Because testing happens live, you can adjust your pattern and immediately see the effect — the fastest way to get a tricky regex right.
Common Regex Patterns
Here are some building blocks that appear in almost every pattern:
\d— any digit (0–9)\w— any word character (letters, digits, underscore)\s— any whitespace (space, tab, newline).— any single character*— zero or more of the previous item+— one or more of the previous item?— zero or one (makes the previous item optional)^— start of the line$— end of the line[abc]— any one of a, b, or c(…)— a capture group
For example, \d{3}-\d{4} matches a pattern like 555-1234, and [A-Z]\w+ matches a capitalised word.
Common Uses for Regex
Validation — Check whether input looks like an email address, phone number, or postal code.
Search and replace — Power a find and replace tool to transform text patterns in bulk, far beyond simple literal matching.
Data extraction — Pull specific pieces — dates, URLs, IDs — out of unstructured text or logs.
Parsing — Break structured text into meaningful parts.
Tips for Writing Better Regex
- Build incrementally. Start with a simple pattern and add complexity, testing at each step.
- Use capture groups to extract the parts you care about, not just to confirm a match.
- Escape special characters. A literal dot must be written as
\., since.matches any character. - Watch out for greedy matching. Quantifiers like
*and+match as much as possible; add?to make them lazy when needed.
Frequently Asked Questions
Is the regex tester free? Yes — it is free, requires no sign-up, and runs entirely in your browser.
Which regex flavour does it use? It uses JavaScript regular expressions, which share syntax with most common regex dialects.
Can I see capture groups? Yes. The tester shows the full match along with each capture group it extracts, so you can confirm your pattern pulls out the right pieces.
Is my text uploaded anywhere? No. All matching happens locally in your browser, so your patterns and test data stay private.
Stop guessing whether your pattern works — paste it into the regex tester and watch the matches light up.