Rourke on Technology

As part of a site overhaul, I moved from date-based permalinks to category-based permalinks. I did this to segment the site by top-level categories, and to improve search engine friendliness. Many people argue that this is a superior permalink structure, but very few point out the downsides.

Broken URLs are the single biggest problem. The initial change isn’t a big deal. I used Dean Lee’s Permalinks Migration plugin to redirect all the old URLs to the appropriate new URLs. Watch out, though: whenever you change a category you will end up with a broken URL that’s the above plug-in does not fix. Also, if you change the name of one of your categories, all of the posts under that category will have changed URLs.

Do you “file” posts in more than one category? If so, this permalink structure will cause your posts to have more than one URL. I looked around a bit and wasn’t able to find any problems this would cause other than in search engine optimization. Search engines don’t like “duplicate content” — and a single page that is presented under multiple URLs certainly looks like duplicate content. If a post has multiple URLs it is likely that it will rank lower on search engine result pages. Further, duplicate content can lower your site’s overall page rank.

Wordpress behaves strangely when a post has multiple URLs. The URLs that refer to posts change — seemingly at random. Everything appeared to be okay when I first moved to the new permalink structure. Wordpress appeared to use a single URL to point to each post. However, when I looked a few days later I noticed that Wordpress was using different URLs to point to the pages in question. As a result, I modified my blog posts so most posts are now in only one category.

I will stick with category-based permalinks, but only because I’m trying to segment my blog by top level category. This change wouldn’t be worth it if I were simply trying to opmimize my search engine rankings. In that case, I’d likely use %YEAR%/%POSTNAME% or %POSTNAME%/%POST_ID%.