4xx errors are well within the realm of SEOs, unlike the 5xx server errors which can often require developer input. The 400 errors are often caused due to a user landing on a page which doesn’t exist or if there is some restriction around who can access a particular page. Websites change and sometimes SEOs can forget to update links, navigations and reference points – but there are plenty of tools on hand to help you identify them and fix them too.
In a rush? I’ve created a quick video which covers the vast majority of the text contained within this guide. If you want to know more about these particular areas, please don’t hesitate to get in touch – always happy to talk about technical on-site SEO with anyone!
Let's delve deeper into 400 errors to get a handle on them
What are the different 400 errors?
The most common is the 400 bad request error, this means an incorrect request has been made to your server to a destination that doesn’t exist or is incorrect. You can also receive a file, asset or page back but your browser may not understand it and potentially serve a 400 – Bad request error too.
From there we can also see a 401 Unauthorised Error, meaning the checks did not qualify the user to see the content – such as an incorrect password or the server has rejected their access by not matching the access criteria.
403 is a Forbidden Error when your credentials will not allow you access to certain areas of the site. This is often provided when you don’t have administration rights or access rights.
404 is the one SEOs are often exposed to, meaning it’s a not found error. SEOs and webmasters will often change URLs, images and old content, which can generate some risk when it comes to missing old destinations. When a user is presented with a link to a missing page, they will often see a 404 error.
How do I find 400 errors on my site?
There are several ways you can identify these errors and put in place fixes to prevent them. The first port of call would be to run a Screaming Frog crawl on the site – this will assess all the URLs you have and flag any that have served a 4xx error. Other tools are available such as SEMRush or SiteBulb who all do a similar job. You can also find any within Search Console via the Coverage button > Excluded then there is a tab called Not Found (404) which will showcase all the pages Google has found.
A slight point of differentiation between Screaming Frog and Search Console, you may find legacy ones in Search Console – as Google crawls websites regularly whereas Screaming Frog is a one-off crawl.
How do you fix 404 errors?
I’ve pivoted this question away from the generic 400 errors and most specifically in 404 not found errors, these are likely the most prominent when it comes to SEO. There are two key ways to fix these sorts of errors, this can be done through either creating a page, image or asset – so that the URL now references an actual object or you can remove the reference of the object from the HTML.
Having 404 errors on your site can cause some issues, such as loading speed issues – if an image is not found on a page it can take a little longer for this to be worked out by your browser – some allow time for the image to be served before it’ll show as not found, delaying the total rendering of the page.
Common ways to trigger 400 errors
- Changing locations, URLs and asset names – this can often be relied upon within the HTML or code of the site, if you remove something, double-check it’s not relied on.
- Changing credentials and access – if you have paywalls or start to introduce them, ensure there is a proper procedure, not allowing users to certain content will create not authorised errors for non-logged-in users for example.
- Hardcoded links – I’ve seen some users hardcode images with variations and dimensions in the URL, when it has been updated or resized, it can lead to a 404 – I try to avoid hard linking and use CMS options which will often dynamically change the link when you change the media (such as WordPress).
I would suggest carrying out a crawl of your site on a regular basis, unfortunately, 404s can be a moving target. Although they are not critical (unless there is a significant amount of not found URLs) you can normally leave it to perhaps once per month, depending on the size of your site.
Keep checking Search Console – these are often the most recently discovered ones with historical data. A 301 redirect is often more beneficial than a 404, the 301 should point users over to a page that is as similar as possible – providing as much value as possible, I’ve seen some webmasters divert all 404s to the homepage, which isn’t a great experience for anyone really (unless the homepage is the next best page of course!)