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Regex Find and Replace

Rewrite text with a regular expression and see the result before you run it on real files.

Test String

Matches & Groups

Matches appear here...

How to Use

The example pattern finds a word typed twice, and the replacement $1 keeps one copy; the fixed sentence appears under Replace Result.
Put your own pattern in the pattern box and your text in Test String; every match is highlighted.
Type the replacement: $1 or $2 for numbered groups, $& for the whole match, $$ for a dollar sign.
Copy the result with the button next to Replace Result.

Frequently Asked Questions

How do I use a capture group in the replacement?

Wrap part of the pattern in parentheses and refer to it as $1, $2 and so on in the Replace with box. A named group is referenced by a dollar sign followed by its name in angle brackets.

Why is only the first match replaced?

Without the g flag a regular expression stops at its first match. Add g to the flags box to replace every occurrence.

Can I write \1 in the replacement, as in sed or Python?

No. This tool follows JavaScript, where the replacement uses $1, and \1 would be inserted literally. Inside the pattern itself, \1 still refers back to the first group, as the example pattern shows.

Is my text sent anywhere?

No. The replacement runs in your browser tab, so logs or customer data you paste stay on your machine.

Regex Find and Replace Online

Updated September 24, 2026 · By Saman

Search and replace with a regular expression is one of the fastest ways to clean up text, and one of the easiest to get wrong on a thousand lines at once. This page opens the Regex Tester with a working example: the Repeated word pattern from the Pattern library, \b(\w+)\s+\1\b, and the replacement $1. The sample sentence comes back under Replace Result with every doubled word removed.

How the example works

(\w+) captures a word, \s+ matches the space or line break after it, and \1 asks for the same word again. The \b at each end stops it from matching inside longer words, so "the theory" is left alone. With the i flag, "This this" counts as a repeat, and $1 keeps the first spelling: "This this is a a typo" becomes "This is a typo".

Replacement tokens

Token	Inserts
`$1`, `$2`	The text of that numbered group
`$<name>`	The text of a named group, such as `(?<year>\d{4})`
`$&`	The whole match
$`	Everything before the match
`$'`	Everything after the match
`$$`	A literal dollar sign

Test before you replace in bulk

Most replace disasters come from a pattern that matches more than you meant. Paste a representative sample, including lines that must not change, and read the highlighted matches before trusting the result. Two traps are common: a greedy .* runs to the last possible match on the line, and without the g flag only the first match is replaced.

Words in other scripts

In JavaScript, \w and \b only know the letters A to Z, the digits and the underscore, so the example misses a repeated "café" or a repeated Persian word. With the flags giu, the pattern (?<![\p{L}\p{N}_])([\p{L}\p{N}_]+)\s+\1(?![\p{L}\p{N}_]) does the same job in any alphabet.

The JavaScript regex tester explains the flags and the engine behind this page, and the URL regex is a good pattern to replace with, for example to turn bare links into Markdown with [$&]($&). The full tool with all 15 ready-made patterns is the Regex Tester.

Guides

Regex for Email Validation: A Practical Pattern and Its Limits No regex can tell you whether an address works. A short pattern catches typos; a confirmation email proves the rest. Regex for Numbers, Phone Numbers and IP Addresses Copy-ready patterns for numeric input, phone numbers and IP addresses, each tested, with notes on where a parser or library does the job better.