The source code for the W3C HTML Validation Service is available under the terms of the W3C Software Copyright.
You can retrieve the code a number of ways:
The most interesting files are currently a CGI script called "check" that does pretty much everything, and possibly also the httpd.conf. (select the topmost revision numbers on these pages to see the most recent revision of each file.)
If you intend to actively mirror the code or and/or contribute patches to the code, you should install and become familiar with CVS; this is the tool we use for revision control (it is also used by the Apache and Mozilla developers, and is generally a good thing to get to know.) More information on CVS is available courtesy of Pascal Molli.
Our CVS base is available read-only, using the CVS pserver authentification:
CVSROOT=:pserver:anonymous@dev.w3.org:/sources/public
password: anonymous
The purpose of making the source code available is partly to allow others to set up mirrors of the service (either publicly or within an intranet behind a firewall), but also to allow us to collaborate on making the service better -- there are many ways the service could be improved but I only have a small amount of time to work on it myself.
Before you will be able to get the code to run, you will need a few things already installed on your system:
If anyone tries to use the code, and succeeds (or fails), please let me know!