This formatter re-indents HTML so the document structure becomes visible: each nested level is indented consistently, block elements start on their own line, and attributes stay with their tag. That turns a wall of minified or CMS-generated markup into something you can actually read and debug — and it is often how you discover an unclosed <div> that was quietly breaking your layout, because the indentation suddenly runs away to the right. The content of <pre> and <textarea> is left untouched, since whitespace there is significant and reformatting it would change what the page displays. Nothing is uploaded, so unreleased page source stays private.
Free, fast, and runs entirely in your browser — no signup, no upload to a server.