XML Schema Validator

This service lets you validate XML documents such as XHTML against the appropriate schemas. It performs a more accurate validation than the W3C validator.

You can validate XML documents by URL, by file upload or by direct input. Furthermore, you can validate fragments of XML documents. You can easily validate the page that is currently displayed in your browser with this bookmarklet.

This software is built around the System.Xml and System.Xml.Schema namespaces in .NET Framework 2.0. It is written in Visual Basic .NET.

If you send XHTML documents as text/html, you should also test them in XHTML Proxy.

Validate by URL

Address:
Schema:
Encoding:
HTML compatibility:

Validate by file upload

File:
Schema:
Encoding:
HTML compatibility:

Validate by direct input

Source:	<?xml version='1.0'?> <html xmlns='http://www.w3.org/1999/xhtml'> <head><title>...</title></head> <body> <p>...</p> </body> </html>
Schema:
HTML compatibility:

Fragment validation is temporarily not available.

Options

Schema

You can select a schema manually or let the validator detect it. Automatic schema detection tries to determine the appropriate schema from the xsi:schemaLocation attribute and the public and system identifiers of the document type declaration. This validator does not download any DTD or schema files, but relies on its own ones.

HTML compatibility

Checks some of the HTML compatibility guidelines. These tests are currently performed:

XHTML elements with an empty content model must use <foo />, not <foo></foo>. (However, a missing space before the trailing / is not detected.)
XHTML elements with an non-empty content model must not use <foo />, but <foo></foo>.
Both xml:lang and lang attributes must be specified with the same value.
Avoid XML processing instructions.
Avoid comments inside style and script elements.
Avoid CDATA sections.
Avoid line breaks and multiple white space characters within attribute values.

Requirements

Only documents can be validated that carry an XHTML namespace declaration (e.g. <html xmlns='http://www.w3.org/1999/xhtml'>).
HTML 4.01 documents can't be validated at all. Don't even try it.
If you want to use character entity references other than the built-in ones <, >, ", ' and &, such as   or Ä, you need an XHTML 1.0 document type declaration. However, it's better to avoid entity references in XHTML.
<meta http-equiv='Content-Type' content='text/html; charset=iso-8859-1' /> or similar encoding declarations are ignored, of course. Use an HTTP header such as Content-Type: application/xhtml+xml;charset=iso-8859-1, a BOM or an XML declaration such as <?xml version='1.0' encoding='iso-8859-1'?>.
If you link to this service via an URL such as <http://schneegans.de/sv/?url=referer>, the client needs to send a proper Referer header.
This validator checks for namespace-well-formedness and namespace-validity, so e.g. <span id='foo:bar'> throws an error.
Supported content types are application/xhtml+xml, application/xml and text/html. This validator does not accept text/xml due to its silly treatment of character encoding. It does not accept application/x-httpd-php either, so if you receive a message such as The response code was '406 Not Acceptable', please fix your server.

Known problems

There are some inconsistencies in the XHTML 1.0 specification. For instance, it is unclear whether the form element is allowed to carry a name attribute.
XML 1.1 is not supported. (XHTML 1.1 is supported, of course.)

Feedback

Don't hesitate to send suggestions and comments to Christoph Schneegans (Christoph@Schneegans.de).

Advantages

The XML support of the W3C validator and its clones such as Validome or the WDG HTML validator suffers from several limitations.

This validator also performs a thorough check of language tags such as de-DE or en-US according to BCP 47.

Björn Höhrmann has prepared some interesting tests. I've incorporated some of them in my own test case collection.

Furthermore, this validator checks for element prohibitions, that can't be expressed in DTDs or schemas, and some of the HTML Compatibility Guidelines.

Schema sources

The following schemas are used: