DTD (Document Type Definition) is a set of rules that defines the structure and elements of an XML document. It ensures that the XML document is well-formed and valid. Checking XML against DTD is important because it helps to ensure that the XML document is compliant with the specified rules and standards, making it easier to process and exchange data between different systems.
There are several tools available for checking XML against DTD. One common tool is xmllint, which is a command-line tool that can be used to validate XML documents against a DTD. Another tool is Oxygen XML Editor, which is a graphical tool that provides a user-friendly interface for validating XML documents.