Regex Tester

Write a pattern, paste some text, and watch the matches highlight as you type — with every capture group (named or numbered) broken out per match, and a live replace preview. A cheat sheet covers where .NET's regex flavor differs from the JavaScript engine running this page.

Pattern

/ /g

i ignore case m multiline (^ $ per line) s dot matches newline

Test text

Replace with ($1, $<name>, $& for the whole match)

Result

Replace preview appears here.

.NET vs JavaScript — same pattern, different engine

Feature	.NET (System.Text.RegularExpressions)	JavaScript (this page)
Named groups	`(?<name>…)` or `(?'name'…)`	`(?<name>…)` only
Replacement refs	`${name}`, `$1`	`$<name>`, `$1`
Dot matches newline	`RegexOptions.Singleline`	`s` flag
Atomic groups `(?>…)`	Supported	Not supported
Backtracking runaway	`MatchTimeout` can cap it; `[GeneratedRegex]` analyzers warn	No timeout — an evil pattern can freeze the tab (including this one)
Comments / free-spacing	`RegexOptions.IgnorePatternWhitespace` + `(?# )`	Not supported

Everything runs in your browser — patterns and text are never uploaded anywhere.