Regex Tester

Regular expressions (regex) are a compact language for matching patterns in text. This tool compiles your pattern with JavaScript's native RegExp constructor — new RegExp(pattern, flags) — and runs input.matchAll() against your text, so it behaves exactly like regex in a browser or Node.js. That means it supports everything the V8/SpiderMonkey engine does: character classes ([a-z]), quantifiers (* + ? {3,5}), anchors (^ $ \b), alternation ((cat|dog)), lookahead and lookbehind, named groups, and Unicode property escapes. Two things are worth knowing about this specific UI. First, it lists only the full match text (group 0) and the index where each match starts — it does not display individual capture groups, named groups, or a replacement preview, even though the underlying matches contain that data. Second, because matchAll is used, you generally want the global g flag to see every match rather than just the first. The pattern field expects a raw pattern, not a /.../ literal, so don't wrap it in slashes. Regex is ideal for structured-but-flat text like logs, emails, and simple delimited formats, and a poor fit for recursive structures like HTML or JSON — reach for a parser there. Matches recompute on every keystroke for fast iteration.