Developer guide

How to validate XML syntax

XML syntax validation checks well-formedness, including one root element, matching tags, valid names, quoted attributes, and correctly formed character references.

Open the XML Validator

Well-formed XML rules

Every XML document needs one root element. Start and end tags must match exactly, including letter case. Attribute values must be quoted, and reserved characters must use valid references when they are data.

Valid structure

<root><item id="1">Text</item></root>

How to validate XML

Paste XML or open a UTF-8 file.
Select Validate XML.
Read the first browser parser error.
Inspect that location and the nearest opening tag or reference before it.
Correct the issue and validate again until the report passes.

Error wording and line details vary by browser. The reported position may be where parsing became impossible rather than where the original mistake began.

Common XML syntax errors

Problem	Example
Mismatched case	`<Item></item>`
Unquoted attribute	`<item id=1/>`
Unescaped ampersand	`A & B`
Multiple roots	`<a/><b/>`

Use & for a literal ampersand in text and place all top-level content inside one document element.

Syntax validation versus schema validation

A well-formed document follows XML syntax. XSD or DTD validation additionally checks allowed elements, attributes, order, types, and relationships defined by a vocabulary.

The ToolPixels validator checks syntax only. It does not validate XSD, DTD rules, or application requirements, and it does not load external documents.

Practical validation cautions

Fix the first error before trusting later locations.
Namespaces can be well-formed but still wrong for an application.
Standard XML entities and numeric references are supported.
DTD and custom entity declarations are not supported here.
Run schema and business validation after syntax passes.

Open the ToolPixels tool

Check XML well-formedness locally and read the browser parser's first error without uploading the document.

Validate XML now