This is an AJAX interface to a Perl script CGI interface to a modified C program I wrote for class at one point. (The Perl script is there for some boring CGI overhead.) It solves Sudoku problems quickly. (Very quickly.) If there are multiple solutions, it will only find one.
The source code for the server-side components is available.
8 - values you provided
8 - values we calculated
8 - impossible value you entered
solve - solves the puzzle
reset - clears the solution squares
clear - clears everything