403 vs 404

Should CMSs auto-generate 403s when URLs change?

Having your CMS or eCommerce system use text-based URLs like this http://www.armiga.co.uk/pandora-style-jewellery/silver-plated-beads/ rather than query-strings like this http://www.armiga.co.uk/products.html?product_sub_category_id=1 can help to increase a page's relevance ranking but there a few possible down-sides, and if the content keeps changing, so do the URLs which can lead to regular '404 page not found' errors.

404 errors are not exactly uncommon and search engines like Google, Yahoo!, Bing, etc should update there listings frequently enough so that most out-of-date links are corrected within a few days, is it it worth trying to avoid them?

Smart 404s

One approach that I've used in the past is 'Smart 404s'. This is where you train your 404 error handler to examine the URL that has been requested and test to see if another version of the page exists and redirect the visitor if there's a match.

This can work very well sometimes if you're inheriting a website and using a completely different URL structure.

Another options is to use Google's 'Enhanced 404 widget' or something similar that picks out the keywords in the URL and runs a relevance match search against an index of your website.

Smarter CMS

There is a way of avoiding 404s in the first place though, and that is to train your CMS to leave a 403 redirect whenever a URL is changed. A 403 redirect is usually a very low impact experience, so much so that most visitors will arrive at the correct page without noticing that they have been redirected. 403s also help search engines pass on relevance 'weighting' that might have been attributed to a page from the old URL to the new version.

These 403 redirects should be part of the system and be able to respond to a string of updates so that when a page is updated 5 times, each of the 5 different URLs that would have been valid, will redirect to the latest live version rather than version 1 redirecting to version 2, 2 to 3 and so on.

That's the theory anyway - time for some implementation...