Regex Replace Tester

Test regex find-and-replace patterns with live preview, match highlighting, and full backreference support.

Try a sample:
/ /g
Flags

Source with matches (0 matches)

Enter a pattern to highlight matches…

Replaced output

About Regex Replace Tester

The Regex Replace Tester lets you experiment with regular-expression based find-and-replace operations directly in your browser. Type a pattern, choose your flags, write a replacement string with optional backreferences, and instantly see both highlighted matches in the source text and the fully replaced output.

It uses the native JavaScript String.prototype.replace engine, so the same pattern that works here will work in your Node.js, browser, or front-end code. All work happens client-side — nothing is uploaded.

It is the perfect companion for cleaning up data, refactoring code, masking sensitive fields, reformatting dates, or any task where you need to transform text by pattern.

How to Use Regex Replace Tester

  1. Enter a pattern in the Pattern field. Use parentheses to capture groups, e.g. (\w+)\s+(\w+).
  2. Write a replacement in the Replacement field. Reference captured groups with $1, $2, named groups with $<name>, or the whole match with $&.
  3. Toggle flags as needed. Turn on g for replace-all, i for case-insensitive matching, m for multiline anchors, s to make . match newlines, and u for full Unicode.
  4. Paste your test string into the Test String box. Matches will be highlighted in yellow and the Replaced output panel will update live.
  5. Click Copy on the Replaced output panel to grab the result, or click any sample preset above to see common patterns in action.

Common Use Cases

Data masking

Replace emails, phone numbers, or IDs with placeholders before sharing logs.

Reformatting

Convert dates from YYYY-MM-DD to DD/MM/YYYY or vice versa.

Refactoring code

Rename variables, swap argument order, or migrate API call signatures across files.

Cleaning text

Strip extra whitespace, remove comments, or collapse repeated punctuation.

Markup conversion

Translate Markdown links, HTML tags, or BBCode to other formats.

Log normalization

Standardize timestamps, log levels, or path separators across mixed sources.

FAQ