JAEN

Regex Replace Tester

Test regex search and replace in real time with match highlights and capture group details.

Input data is processed in your browser
Data is never sent to a server

Tool

Use $1, $2 … to reference capture groups

or drag & drop a file

Quick Reference

Patterns

.any character except newline\ddigit [0-9]\wword character [a-zA-Z0-9_]\swhitespace^start of string / line$end of string / line*0 or more+1 or more?0 or 1 (optional){n,m}between n and m times(abc)capture group(?:abc)non-capturing group(?<name>)named capture group[abc]character classa|balternation (a or b)

Replacement tokens

$&entire match$1 $2capture group 1, 2, …$<name>named capture group$'string after match$`string before match$$literal $

What is Regex Replace Tester?

Regex Replace Tester lets you interactively build and test regular expression search-and-replace operations in real time.

It highlights matches in the source text, shows each match’s index, length, and capture groups in detail, and displays the final replaced string — all at once as you type. The built-in quick reference for patterns and replacement tokens makes it useful for both debugging and learning regex.

How to Use

  1. Enter a regex pattern in the pattern field (no slashes needed).
  2. Toggle flags (g, i, m, s) with the flag buttons.
  3. Enter a replacement string — use $1, $2 to reference capture groups.
  4. Type or paste your test string to see highlights and the replacement result instantly.

FAQ

Which flags are supported?

g (global — find all matches), i (case-insensitive), m (multiline — ^ and $ match line boundaries), and s (dotAll — . matches newlines).

How do I reference capture groups in the replacement?

Use $1, $2, … for numbered groups, $<name> for named groups. $& inserts the entire match, $` inserts the text before the match, and $' inserts the text after the match.

Are zero-width matches handled correctly?

Yes. Zero-width matches like ^ and lookaheads are handled safely to prevent infinite loops during global replacement.

Is my data sent to a server?

No. All processing uses the JavaScript regex engine running entirely in your browser.

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