Measuring the effectiveness of your redirects
When I work on a site migration I like to redirect everything I possibly can find, very much in a 'no one gets left behind' sort of way. Most migration projects don't do this, for a multitude of reasons, but years ago I was told to only redirect the top 200 pages of a site which was about 10% of the live pages. I did strongly voice an opinion on this but, had discussions, but ultimately was firmly told I was wrong. Inevitably the site lost 66% of its traffic for several years following that migration. Now this is part of my processes that I do not take any short cuts with.
So how important are redirects? If you look in your Google Search Console at any page you can find where they found links to a page. Sometimes it can be a URL on your site that vanished many years ago and isn't even in the Google index. This usually means there is a page out there somewhere on the web with a link to the old URL on it. Googles bots find these and add these old URLs as incoming links. If you followed Sir Tim Berners-Lee’s advice Cool URIs Don't change and never changed any of your URLs, this will not be a problem. You do do that, don't you though?
The thing is you don't really know where all the backlinks to your site are. No-one has a complete database of the whole internet - it's just to big.
Tracking 404's
To mitigate these issues I track incoming traffic that arrives at my 404 page. I have set this up as a Fathom event - read how I did that here and I also track this page with Google Analytics - the only page on the site where I use it. The reason for the GA4 is that I switched to fathom but initially had no way to track the 404s so kept the GA4 tracker on there. I built a Looker Studio dashboard using that data and still find that handy to look at now and then so the code is still there.
As I already have most of my old URLs redirected it means the URLs are usually misspellings, or badly formed links.
LLMs hallucinating urls
I have noticed recently that I am getting 404 URLs that never existed and these appear to be coming from LLMs hallucinating URLs on my site. This is a concern but with regular checks of the 404's I can mostly set up suitable redirects. I don't however have any context where the link was created - so it is a bit of guess work.
How often do people arrive at my site using an old URL though? I was wondering this so have set up an experiment to track this by utilising UTMs in my redirects.
Using UTM's in redirects
I use Fathom analytics and it has a section in the dashboard for Campaign tracking. This is normally used for marketing campaigns where you want to track effects of adverts. Campaign Source Medium Content Term
Currently I have set the UTM tracking up as: source=redirect medium=301 campaign=simoncox.com content= last part of the old URL
/blog/swanage-belle /post/2011-10-16-swanage-belle/?utm_source=redirect&utm_medium=301&utm_campaign=simoncox.com&utm_content=swanage-belle 301
I have not used the whole old URL because of some concerns over parsing the forward slashes and some other characters that creep in, though might change this - I should at least experiment!
Anecdote alert: Many years ago I tracked all the links on a home page as someone had surmised that the links at the bottom of the page got no traffic - actually they did and more than those in the middle of the page!
UTM examples for redirects
Looking back through my extensive set of redirect for my own site I realise now that it would have been helpful to keep a record of where I found the URLs to redirect from. However in future I will use the campaign field for where I found the redirect. Potentials for the campaign field include: campaign=archives campaign=GSC campaign=Bing campaign=Semrush campaign=Ahrefs campaign=404
For wholesale directory changes, for example I have kept my articles in several different directories over the years, I use Cloudflare's 'splat' redirect to change the directory - the last part of the URL has remained the same. For these I have used the content field to indicate which redirect rule was firing. I wholesale moved /article/ to /post/ and have this in my redirects file:
/article/* /post/:splat?utm_source=redirect&utm_medium=301&utm_campaign=simoncox.com&utm_content=articleSPLAT 301
Google Analytic UTMs
Most of you will be using GA4 for your analytics and that has a larger set of parameters available that you can customise to track what you need.
- utm_id: Campaign ID. Used to identify a specific campaign or promotion. This is a required key for Google Analytics data import. Use the same IDs that you use when uploading campaign data.
- utm_source: Referrer, for example: google, newsletter4, billboard
- utm_medium: Marketing medium, for example: cpc, banner, email
- utm_campaign: Product, slogan, promo code, for example: spring_sale
- utm_source_platform: The platform responsible for directing traffic to a given Analytics property (such as a buying platform that sets budgets and targeting criteria or a platform that manages organic traffic data). For example: Search Ads 360 or Display & Video 360.
- utm_term: Paid keyword
- utm_content: Use to differentiate creatives. For example, if you have two call-to-action links within the same email message, you can use utm_content and set different values for each so you can tell which version is more effective.
- utm_creative_format: Type of creative, for example: display, native, video, search but utm_creative_format isn't currently reported in Google Analytics properties.
- utm_marketing_tactic: Targeting criteria applied to a campaign, for example: remarketing, prospecting but utm_marketing_tactic also isn't currently reported in Google Analytics properties.
Conclusion
So far since installing these UTMs I have not had that many hits on the redirects so they may not be as important as I considered, but I will leave it for a year or two before making any claims – and of course everything in SEO will have changed again. THis does not give me any insight into how Google are processing any old links they find but resolving them to the correct content can only help.
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