Fortunately, the W3C freely distributes the source code for its validation tools. In this tutorial, we're going to use the Debian GNU/Linux operating system to set up a standalone markup validation server.
Read it here
An unused older computer may be used as a server in this case; Debian has minimal system requirements and has excellent compatibility with a huge range of hardware and architectures. In my case, I installed the server as a VMware Server guest running on a box that hosts several virtual private servers on my home development network. You could just as easily apply these instructions to a Sun xVM VirtualBox environment, as long as you specify bridged networking for the virtual machine. It will need to be on the same network segment as your development systems, unless you set up a router to connect multiple network segments.