XML Validator

Well-formed means the syntax is correct: one root element, every tag closed, tags properly nested, attributes quoted, special characters escaped. Valid means it also conforms to a schema that says which elements may appear where, with what attributes and in what order. This tool checks the first and not the second. A perfectly well-formed document can still be rejected by the system you send it to.

Because it comes straight from your browser's XML parser rather than from a custom checker. Chrome, Firefox, and Safari each phrase their parse errors differently, and some of them are terse to the point of unhelpful. What is consistent is the location: the error names the line and the construct where the parse failed, which is usually enough to spot the unclosed tag.

Because in XML an ampersand always starts an entity reference, so a bare & in text content is invalid unless it is escaped as &amp;. HTML parsers are forgiving about this and XML parsers are not, which is why content copied out of an HTML page so often fails here. The same goes for a bare < in text, which must be &lt;.

Only the whitespace between elements. It re-indents with two spaces per level using a string transform, so self-closing tags stay self-closing and an element with inline text stays on one line. It does not re-serialise the document through the DOM, which would otherwise rewrite <br/> as <br></br> and reorder your attributes.

You can check that it is well-formed, which catches the most common breakages: an unescaped ampersand in a URL, an unclosed <url> element, a stray character before the declaration. What it cannot tell you is whether you have used the right elements for the sitemap or RSS schema, since that needs schema validation against the specific spec.

Paste it into the box on this page. There is no button and no upload: the document is parsed on every keystroke, and the status line either confirms it is well-formed or shows the first parse error. Fix that error and the check re-runs immediately, which makes working through a broken file quick.

No. The parsing uses the DOMParser built into your browser, so the document stays on your device and the page keeps working with the network disconnected. That is the reason this is safe for a config file, an internal API payload, or anything else you would not paste into a hosted validator.

Because XML parsing stops at the first fatal error by design. That is in the specification, not a limitation of this tool. It also means the second error is often an illusion: an unclosed tag near the top of a document makes everything below it look wrong, and fixing the first frequently clears several apparent problems at once.

No, there is no file picker. Open the file in any text editor, copy the contents, and paste them in. For very large documents that is worth knowing in advance, since the check re-runs on every keystroke.