Regex Replace Tool – Find and Replace Text Using Regular Expressions
About the Regex Replace Tool
The Regex Replace Tool lets you search a block of text with a regular expression and replace every match in real time. Type a pattern and a replacement string, and the output updates instantly as you type, no submit button required. Captured groups are fully supported, so a pattern like (\d{3})(\d{3})(\d{4}) paired with a replacement of ($1) $2-$3 can reformat a string on the fly using $1, $2, and similar group references.
Five toggleable flags give you control over exactly how the pattern matches: global for replacing every occurrence instead of just the first, case-insensitive, multiline so ^ and $ match line boundaries, dot-all so a period also matches line breaks, and unicode for patterns that need to handle a wider character range. A built-in library of ready-made patterns covers common jobs like collapsing extra whitespace, stripping HTML tags, or removing duplicate words, so you don’t have to write every expression from scratch. If you’re cleaning up scraped or copy-pasted content, running it through the Remove Duplicate Lines tool first can clear out repeated rows before you fine-tune the text with a regex pattern.
Once your replacement is done, checking the before-and-after with the Text Diff Checker is a fast way to confirm exactly what changed. Because a wrong pattern can quietly rewrite more of your text than intended, every match runs against your source text live, with a stats panel showing the replacement count and character totals so nothing changes without you seeing it happen.
BigToolSite.com verified this tool by testing capture groups, all five flag combinations, and every quick-replacement template against real-world sample text to confirm the counts and output stayed accurate.
How to Use the Regex Replace Tool
- Enter your regular expression in the Search Pattern field.
- Enter your Replacement String, using
$1,$2, etc. to reference captured groups. - Toggle the flags you need: g (global), i (case-insensitive), m (multiline), s (dot-all), or u (unicode).
- Paste or type your text into the Source Text box, or pick a Quick Replacement Template to auto-fill a common pattern.
- Review the live Replaced Output and the stats panel for match count, original length, new length, and characters changed.
- Use Copy Output or Download .txt to save the result, or Clear All to start over.
Example Usage
Pattern: \s+ Replacement: (single space) Flags: g
Input: “This text has irregular spacing”
Output: “This text has irregular spacing”
For a group-based example, a pattern of (\d{3})(\d{3})(\d{4}) with a replacement of ($1) $2-$3 turns “5551234567” into “(555) 123-4567” in a single pass, which is one of the built-in Quick Replacement Templates. Before running a slug-style pattern, formatting the source text with the Case Converter can make lowercase-only patterns like the “Convert to Slugs” template match more predictably.
Frequently Asked Questions
Without it, the regex only replaces the first match it finds. With the global flag enabled, every matching instance in the source text is replaced, which is why it’s turned on by default.
Wrap the part of your pattern you want to reuse in parentheses, then reference it in the replacement field as $1 for the first group, $2 for the second, and so on. This is how patterns like phone number reformatting work.
The tool detects the syntax error immediately, highlights the pattern field in red, and displays the exact error message so you can fix it without guessing.
Multiline changes how ^ and $ behave, matching the start and end of each line instead of the whole string. Dot-all changes how the . character behaves, letting it match line breaks as well as regular characters.
Yes, it’s fully browser-based with no signup required, and none of your text is uploaded to a server since all processing happens locally.
