XML is still common in enterprise APIs, RSS feeds, mobile configuration, office documents, and legacy integrations. It is more verbose than JSON, but it is also precise. A good XML formatter helps you see that precision by making nesting, attributes, and text content easier to inspect.

Every tag must close correctly

XML requires a matching closing tag for every opening tag unless the element is self-closing. A document with <item><name>Ada</item> is invalid because name never closes. Formatters make this kind of mismatch easier to locate because the indentation suddenly stops matching the expected tree.

Attribute values need quotes

XML attributes must be quoted. Both single and double quotes are allowed, but leaving quotes out is not. For example, <user id="42"> is valid, while <user id=42> is not. This matters when XML is generated from templates or copied from documentation examples.

Escaping is different from HTML habits

Characters like &, <, and > have special meaning in XML. If they are part of normal text, they need to be escaped. A raw ampersand in a company name or query string can break an entire document even when the rest of the file looks correct.

Namespaces change element identity

XML namespaces prevent collisions when multiple vocabularies appear in the same document. The prefix is not just decoration. atom:title and media:title can mean different things even if both end with the word title. When debugging, check namespace declarations near the root element before assuming two fields are equivalent.

Whitespace can matter

In many XML documents, whitespace between elements is only formatting. In mixed-content documents, whitespace can be part of the text. This is common in document formats where text and inline markup are interleaved. Formatting is useful, but be careful when changing XML that treats whitespace as content.

Validate when a schema exists

XML can be validated with DTD, XSD, or other schema systems. If an integration partner provides a schema, use it. Formatting will show whether the document is readable and well-formed, while schema validation checks whether the document follows the contract expected by the receiving system.

Use formatting as a debugging step

When an XML API rejects a request, format the request body first, then check closing tags, attributes, namespaces, escaped characters, and required elements. This sequence catches the common mistakes before you spend time investigating network settings or authentication.