What does the multiline flag change?

Without it, ^ and $ match only the very start and end of the whole text. With it, they match at the start and end of every line — which is what you usually want when searching a list or a log file.

My pattern is very slow or the page freezes — why?

Nested quantifiers like (a+)+ can cause catastrophic backtracking, where the engine tries an exponential number of combinations. It's a property of the pattern, not the tool. Simplify the nesting, or make the inner quantifier possessive by restructuring it.

Regex Tester

Write a pattern and see exactly what it matches. Every match is listed with its position in the text and the contents of each capture group, including named groups — which is usually what you actually need when a pattern nearly works but not quite. Case-insensitive, multiline and dot-matches-newline flags are all switchable.

Your text

Pattern

Ignore case (i)

Multiline — ^ and $ match each line (m)

Dot matches newlines (s)

Result

Enter a pattern to start matching.

Nothing is uploaded — this tool runs inside your browser, so your files never leave your device.

Help us improve

Why use this tool

Lists every match with its position in the text
Shows numbered and named capture groups for each match
Toggles for the i, m and s flags
Reports an invalid pattern clearly instead of failing silently

How it works

1Paste the text you want to search.
2Type your pattern and set any flags you need.
3Read the matches and capture groups underneath.

Regex Tester — frequently asked questions

JavaScript's, since it runs in your browser. It's very close to PCRE for everyday patterns, but lookbehind is only supported in newer browsers and there is no \A or \z anchor — use ^ and $ with the multiline flag off.

More developer tools

Text → Base64 Base64 → Text URL Encoder URL Decoder JSON Formatter JSON Minifier

Looking for something else? Browse all developer tools

Explore the other tools

Same deal everywhere on the site — free, no sign-up, and no watermark on anything you download.

QR Code Tools Barcode Tools PDF Tools Image Tools SEO Tools Text Tools Calculators Unit Converters Color Tools File Tools Business Tools AI Tools Utilities

Or see every tool on one page.