Validates the URL used and if not matching the official permalink then it issues a HTTP 301 or HTTP 404 message.
WordPress 2.3 now includes validation of the permalink URL when using Apache web server, but if using IIS then this plugin is still relevant.
Permalink Validator helps Search Engine Optimization (SEO) as it prevents duplicate contents on your WordPress blog:
WordPress it very forgiving when supplying an URL that doesn't match the actual permalink to a post or a page. This is caused by WordPress using some very greedy wp_rewrite_rules, which accepts almost any URL as valid.
This means that multiple URLs could be used to reach the page, which search engines sees a duplicate content and leads to penalty.
For example it will accept the following permalink URL as valid:
Even though the official URL is this:
Permalink Validator makes a hook to template_redirect, and then adds some extra validation of the URL supplied before actually calling the theme-templates.