XML Validator

Altova® XMLSpy® includes the industry’s most standards-conformant XML validator and an informative validation window for locating, viewing, and troubleshooting errors. XMLSpy includes numerous features for helping you create valid XML documents quickly and easily. Intelligent editing features such as context-sensitive code completion and entry helper features offer you valid choices based on the content model and your location in a document, and the new, improved validation window offers detailed information about any validation errors in your XML document or project file. It supports validating any XML file based on its associated DTD or XML Schema. The granular details provided by the XMLSpy XML validator make troubleshooting and XML project management considerably faster and more effective.

http://www.altova.com/products/xmlspy/create_valid_xml_validation.html