Does this validate against an XSD?
No. This tool performs a well-formedness check only. There is no XSD validation, no DTD validation and no namespace validation. A document can be reported as well-formed and still be wrong for your schema, because a missing required field, a misspelled element name or an unexpected value are all structurally legal XML. Convert the document to JSON and validate it against a schema if you need that level of checking.
What does well-formed actually mean?
It means the text is readable as XML: exactly one root element, every start tag closed by a matching end tag with the same name and case, every attribute value quoted, every entity declared, and every character legal. That is a check of the markup itself, not of whether your data makes sense.
Does this upload my XML?
No. Parsing, validation and formatting all run locally in your browser. Your XML is never uploaded to TechFixGen servers, is not saved to browser storage, and is not included in analytics events.
Will formatting change my text content?
Whitespace between elements is character data in XML, so indenting a document that has no inter-element whitespace does add whitespace to its text content. That is what formatting means here. No visible text is ever altered, reordered or reflowed: every text node that is not formatting whitespace comes back character for character.
Are comments, CDATA and processing instructions preserved?
Yes, all three. Comments are printed back as comments, CDATA sections stay CDATA so their raw markup is not re-escaped, and processing instructions such as <?xml-stylesheet?> keep their target and data.
Why are mixed-content elements left on a single line?
Because adding a line break next to real text would insert a newline into that text. An element such as <p>Hello <b>world</b>!</p> mixes character data with child elements, so it is left exactly as written and only its child elements are formatted in turn. Prose is never re-wrapped.
Are namespaces and prefixes preserved?
Yes. Namespace declarations such as xmlns and xmlns:atom, prefixed element names, and prefixed attributes such as xsi:type are all printed back with their original prefixes and in their original order. The formatter never renames, adds or removes a namespace.
Is the XML declaration preserved?
Yes, exactly as you wrote it, including its encoding attribute and any byte-order mark. It is copied from your source text rather than regenerated, so an unusual or older declaration survives untouched.
What happens with DOCTYPE and ENTITY declarations?
They are refused before parsing begins. A DTD can declare entities, and an entity can reference a URL, which is the mechanism behind billion-laughs and XXE attacks. The document is never parsed, no entity is ever expanded and no network request is ever made. Keep the declaration and validate it with a tool you control if you genuinely need one.
Which indentation width should I use?
Two spaces is the common convention for feeds, sitemaps and config files. Four spaces is easier to spot by eye in deeply nested documents. Either is fine — what matters is that the document ends up consistent, since a file with mixed indentation is itself a common source of bugs.
Why is the error message different from another tool's?
The message and the line and column come from your own browser's XML parser, because that is what reads the document — the tool never sends it anywhere to be checked. Chrome, Edge, Firefox and Safari word their reports differently, and some omit a position entirely. The surrounding guidance is the same in every browser.
Can this fix my XML automatically?
No. It explains the error and points at the line and column when your browser supplies one, but it never rewrites your data to make it parse. Correcting the input by hand is the safe, predictable way to resolve a syntax problem.