Regex Replace Tester

Enter a pattern, flags, replacement string, and source text to preview first-match or global replacement without blocking the main UI.

Pattern

Flags

Replacement

Replace all matches by adding g

Source text

Replacement result

ReadyUses native JavaScript replacement-string semantics such as $&, $1, and named-group substitutions.

Replacement match & capture evidence

See exactly which spans matched, which capture groups were populated, and what replacement each match contributes before reusing the expression.

Maximum matches to inspect

—Matches

—Capture groups

—Inspection time

—Output changed

#	Index	Match	Captures

This page executes JavaScript RegExp semantics in your browser. PCRE, RE2, .NET and other flavors can differ.

Before reusing a regular expression

keeps the established regex widgets and worker-guarded execution paths intact while connecting testing, explanation, extraction, replacement, test cases, static risk review, and code generation. Pattern data stays in the browser, and the shared inspector can save an explicit pattern locally.

Regex flavor and performance boundaries

Interactive checks follow the JavaScript RegExp implementation available in the current browser unless a tool explicitly says otherwise. Token explanations and backtracking warnings are bounded static guidance, not PCRE/Python/.NET compatibility, formal complexity analysis, or proof that a pattern is safe for every possible input.