Regex Replacement Tester
Test JS regex substitutions: $1, $&, $<name>, and \U/\L/\u/\l case tokens. Live before/after.
Result (2 matches)
Capture groups
#1
full: ada@banksalad.com
$1: ada
$2: banksalad.com
#2
full: alan@princeton.edu
$1: alan
$2: princeton.edu
Regex Replacement Tester — Free Online Tool
Tests JavaScript regular expression substitutions interactively, applying a replacement string with capture-group references ($1, $2, named groups) and function replacements to a sample text, with a live before / after diff and match highlighting, useful for prototyping sed-like transforms, building search-and-replace rules, and verifying backreference behavior across engines.
How to use the Regex Replacement Tester
- Open the tool above — it runs entirely in your browser, so your input never leaves this page.
- Paste or type your input into the field, then press the relevant button (e.g. Encode / Decode, Generate, or Convert).
- Copy the result from the output area with the copy button orCtrl/Cmd + C.
- No signup, no upload, and no tracking — repeat as often as you need.
Frequently asked questions
Is the Regex Replacement Tester free to use?
Yes. The Regex Replacement Tester is completely free, with no signup, no ads inside the tool, and no hidden limits.
Does the Regex Replacement Tester upload my data?
No. The Regex Replacement Tester processes everything locally in your browser. Your input is never sent to a server, so it stays private even on shared devices.
Does the Regex Replacement Tester work offline?
After the page loads, the Regex Replacement Tester runs entirely in your browser, so it keeps working without a network connection.
Free & private — why use this Regex Replacement Tester
The Regex Replacement Tester runs 100% client-side in your browser. Your data is never uploaded to a server, no account is required, and the tool is completely free. It works offline once the page has loaded and is part of a growing collection of privacy-first developer utilities.