When your permalink structure does not end by a trailing slash (/), all your links look like http://example.com/2009/05. Permalink Trailing Slash Fixer add the missing trailing slash. Example If you have a site with the following permalink structure /%category%/%postname%.html and your permalinks look like these: Single Post: http://example.com/my-category/sample-post.html. Category: http://example.com/my-category. Archive: http://example.com/2009/05. Page: http://example.com/about. After activation of the plugin: Single Post: not modified. Category: http://example.com/my-category/. Archive: http://example.com/2009/05/. Page: http://example.com/about/.