Regex Find and Replace — Online JavaScript Regex Replace Tool

What is Regex Replace?

Regex find-and-replace is what makes regular expressions genuinely productive — one small pattern can rewrite thousands of lines. This tool follows the exact rules of JavaScript's String.prototype.replace(regex, replacement): all six flags (g, i, m, s, u, y) are supported, and every replacement-token JS supports is honored — $1 through $99 for numbered groups, $<name> for named groups, $& for the whole match, $` and $' for the pre/post-match context, and $$ for a literal dollar. Beyond raw JS, this tool also expands \n, \t, \r, and \\ in the replacement string so 'insert a newline' works the natural way, and it emits a per-match trace panel so you can spot 'why did that one line come out wrong' without instrumenting your own code.

How to find and replace with regex online

1. 1Type your pattern in the Pattern field (no wrapping slashes needed).
2. 2Toggle flags — 'g' (global) is on by default so every match is replaced.
3. 3Enter the replacement, using $1..$n for capture groups, $<name> for named groups, and \n / \t for newlines / tabs.
4. 4The output pane and match-detail panel update live. Copy the output when you're done.

Use Cases

Code Examples

// Rewrite "John Smith" → "Smith, John"
const out = input.replace(/(\w+) (\w+)/g, "$2, $1");

import re
out = re.sub(r"(\w+) (\w+)", r"\2, \1", input)  # \1 \2, not $1 $2

# GNU sed - Extended regex with -E; & is the whole match, \1..\9 are groups
sed -E 's/(\w+) (\w+)/\2, \1/g' file.txt

Key Concepts

Backreference

In the replacement string, `$1` inserts what capture group 1 matched. Named groups use `$<name>`. In the pattern itself, use `\1` to require a repeated match.

Escape sequences in replacement

Unlike the pattern, JavaScript's replacement string does not natively interpret \n or \t. This tool expands them for you so typing `\n` inserts an actual newline.

Global vs single replace

The `g` flag replaces every match. Without `g`, only the first match is replaced — the standard behavior of `String.replace`.

Tips & Best Practices

• ▸Test the pattern first in the Regex Tester if you're unsure it matches what you think — 'wrong pattern' is a more common bug than 'wrong replacement'.
• ▸For huge replacements across many capture groups, name the groups (`(?<year>\d{4})`) and reference them by name — the intent is easier to read months later.
• ▸If your replacement text contains a literal `$`, escape it as `$$`.
• ▸Regex replace is not the right tool for HTML or JSON transforms — use a parser. Regex is fine for CSV, log, and plain-text transforms.
• ▸Enable case-insensitive `i` for text tasks like 'replace every occurrence of company name' — English text mixes case unpredictably.