Puffin's XML Formatter & Validator is a free browser tool for cleaning up and checking XML. Paste a document, drop an .xml file, browse from disk, load a sample, or point at a public URL — then Process to pretty-print and validate. SVG, RSS, and other XML documents work the same way.

The checker enforces well-formedness: one root element, case-sensitive tags that match, quoted attributes, legal references, and declared namespace prefixes. It reports each problem with its line and column. Warnings cover a missing XML declaration, an unusual encoding, and a document type — this tool does not validate against a DTD or schema.

With Fix XML enabled, the tool closes unclosed tags, drops stray end tags and duplicate attributes, quotes attribute values, and escapes a bare < or &. A document that does not have exactly one root is wrapped in <document>. Indentation is added between elements. Text, CDATA, and anything inside xml:space="preserve" stay as written. Nothing is uploaded to a server — processing runs in your browser (URL fetches are the exception, and may fail when the remote host blocks cross-origin requests).