xmlhack: RNV: C-based Relax NG validator

RNV is a command-line tool for validating XML documents against schemas written in Relax NG compact syntax. Developed by David Tolpin and written in portable ANSI C, it's fast, lightweight, and provides very good reporting about validity errors in documents.

RNV [download] requires Expat for document parsing, but otherwise has no other dependencies and should build right out of the box on most platforms. It comes bundled with two other tools:

ARX, a tool to automatically associate an XML document with a Relax NG schema, based on the document's filename and contents

RVP (Relax NG Validation Pipe), a tool designed to "ease embedding of a Relax NG validator into various languages and environments."

The release distribution contains a readme file that provides documentation for all three tools.

RVP, is in fact, a tool for RNV, not any validator. It wraps RNV into a text-based protocol so that it can be used with any language that can write and read strings.