Regex Replace Tester

How to use

1. 1Type or paste a regular expression into the pattern field.
2. 2Toggle the g, i, m, s, u, and y flags to match the behavior you want.
3. 3Type a replacement template. Use $1, $2 for numbered captures, $<name> for named captures, and $& for the whole match.
4. 4Paste the sample text you want to run the replacement on into the test area.
5. 5Read the live result, the match count, and the per-match breakdown to confirm each substitution is what you expect.
6. 6Open the Use-this-in-code panel and copy the JavaScript, Python, or sed snippet to paste straight into your codebase.

About this tool

Regex Replace Tester is a focused sandbox for testing regular expression substitution patterns before pasting them into code. Type a pattern, pick the g, i, m, s, u, and y flags, type a replacement template, and paste any sample text. The tool compiles your pattern with the same JavaScript RegExp engine your code will run, applies the replacement, and shows the final output, the count of replaced matches, and a per-match breakdown that lists each match, every numbered and named capture group, and the exact replacement string that match produced. Replacement template syntax follows the JavaScript String.prototype.replace rules and is fully documented on the page: $& for the whole match, $` for the text before the match, $' for the text after the match, $$ for a literal dollar sign, $1 through $99 for numbered capture groups, and $<name> for named capture groups declared as (?<name>...). The result panel honors your flag choice, so removing the g flag replaces only the first match the way the engine does at runtime. Quick samples cover the substitutions developers reach for most often: rewriting ISO dates to US format, obfuscating email addresses, formatting US phone numbers, swapping first and last names, wrapping matches in HTML tags, and stripping tags from a snippet. The Use-this-in-code panel exports your tested pattern and replacement as a ready-to-paste JavaScript replace call, a Python re.sub call (with JavaScript replacement tokens translated into Python backreference syntax), and a sed -E command (with numbered backreferences translated and unsupported features flagged) so the tested expression goes straight into source code or a shell pipeline. Pattern errors surface inline as you type, and runaway empty-match loops, oversized inputs, and runaway match counts are bounded so the page stays responsive. Everything runs locally in the browser: the pattern, replacement, and test text never leave your device, which makes the tool safe for debugging substitutions against confidential logs, customer data, or production strings.

Free to use. Works in your browser. No signup, no login.