I am planning to build a broken link checker tool for websites. Can you guys please let me know which tools I need to use in building the tool. I have experience in JavaScript, ExtJS, jQuery and PHP. Any help/suggestion would be greatly appreciated.
Have a look at this WP plugin:
http://wordpress.org/extend/plugins/broken-link-checker/ [Broken Link Checker]
It already does the job.
You could either reverse engineer it or use it as a concept tool to make your own