How the XML / XSD Validator Works

What the Tool Does

This XML XSD validator checks XML documents against XML Schema definitions using server-side processing. The tool validates structure, data types, element ordering, and attribute requirements defined in your schema. When validation fails, it reports specific errors with line and column numbers when available. The validator handles namespaces, complex types, sequence constraints, and schema facets like pattern matching and value restrictions.

Example: Book Catalog Validation

Consider this XSD schema requiring books to have integer IDs and decimal prices:

<xs:element name="book">
  <xs:complexType>
    <xs:sequence>
      <xs:element name="title" type="xs:string"/>
      <xs:element name="price" type="xs:decimal"/>
    </xs:sequence>
    <xs:attribute name="id" type="xs:integer" use="required"/>
  </xs:complexType>
</xs:element>

Invalid XML like <book id="abc"><price>not-a-number</price></book>would fail validation with type constraint errors for both the ID attribute and price element.

Common Use Cases

Developers use XML Schema validation when integrating with SOAP APIs, validating configuration files, or processing data interchange formats. Common scenarios include validating API responses against published schemas, checking configuration files before deployment, and ensuring data quality in ETL pipelines. The validator is particularly useful for catching type mismatches, missing required elements, and incorrect element ordering before data reaches production systems.

Validation Engine and Limitations

This tool uses libxml2 through the libxmljs Node.js binding, providing XML Schema 1.0 compliance. The validator processes schemas entirely server-side for security and does not fetch external resources or resolve network-based imports. External entity processing (XXE) is disabled for safety. Schema includes and imports work only if all referenced schemas are provided in the main XSD content.

• Network access: Blocked for security
• Schema imports: Must be inline, no external resolution
• External entities: Disabled (XXE protection)
• Processing limits: Reasonable size limits apply

Server-side vs Client-side Processing

Client-side XML well-formedness checks are sufficient for basic syntax validation. However, XSD validation requires a specialized engine because browsers don't include XML Schema processors. Server-side validation ensures consistent results, handles complex schema features like inheritance and imports, and provides security isolation from potentially malicious XML content.