When you or a robot accesses a page, a hidden element are the headers – these are viewable with the right tools (which are built into most browsers) getting these right are essential for SEO and page speed.
Typically most pages you access return a simple header of a 200 – telling search engines or users that this is a valid document (or resource). A 200 simply means “OK” when the a url matches a document it returns a 200 saying yep – this is the right page. Search engines interpret this as a valid page which should be indexed.
The opposite of a 200 is a 404, this means that the server isn’t sure what to return, doesn’t know what page or resource you need it is essentially an I do not know but typically called “Not Found”. A 404 often means a page has moved or has been deleted, which isn’t the correct status for either. A search engine when it finds a 404 will revisit this page as it could have been a mistake intermittently, this means you are wasting crawl budget.
To tell search engines you have moved a page permanently a 301 is the best response – this is called a permanent redirect and so search engines move the ‘juice’ or page rank value to this new location, and when pages or domains are moved or consolidated this is often the best status code to use. Search engines will also not check the old location frequently as this is assumed to be a permanent change.
To tell a search engine that it is a temporary change, we would use a 302 – this has less SEO impact and tells search engines that this isn’t permanent so check back with the original location rather than the redirected location. Redirects often default to a 302 unless explicitly told to use a 301, so always worth checking.
Gone, this is similar to a 404 but rather than a “I don’t know” it is more like this is now gone permanently, it has the advantage that search engines now will not keep checking back (too often) and the page will rapidly disappear from the index – this will get rid of a page and cached copy quicker than the more ambiguous 404. Accidentally using a 410 will have bigger issues and you will typically have to resubmit this page manually.
One small problem with a 200 is that it doesn’t give the search engine or user any idea about whether they can reload it from the cache, this means that resources and pages are reloaded including images and scripts (search engines and users do cache, but we can help them a bit, speeding up page loading and indexation) the 304 – not modified – this means that since you last checked the file it hasn’t changed, incredibly useful for large resources such as j query and larger images that are used across a website. Successfully using a 304 can significantly improve indexation and reduce load on servers.
If the website is down, maybe due to exceeding the servers resources or” due to maintenance – use a 503 which means this is temporary, check back. Of course if you have a 503 for too long this is incredibly dangerous to your organic visibility, but is better than any other status if your website is down temporarily.
This deserves a post of its own, but this is where a website is using the wrong status of a 200 instead of a 404, it sounds like a minor issue but it can cause significant indexation and canonicalization issues for Google resulting in a poor user experience and poor indexation of your site, URL re-writing is the most common culprit so make sure that ecommerce catalogues in particular use the right headers.
Headers can contain more than just the status code, they can include the pages canonical, robots instructions and even hreflang. Data which is typically included in a metatag within the head – this has the advantage of being available to search engines before the page is even loaded up and can potentially be included in pages where access to the metadata isn’t possible. This can often be achieved globally, which means that all pages are given the same instructions which is useful for test servers and where global rules make sense. A good example are PDF files, being able to restrict access or canonicalise them has the advantage of resolving versioning issues that some users have.
I think one of the best use of the header is for job adverts if you are an agency looking for technically savvy people, Moz.com did this… not sure how many applicants they had.
How do I check headers?
The easiest way is with this bookmarklet
The harder, but more revealing way is to use Chrome, inspect element, to access this I use the keyboard short cut on the page I am on of Ctrl + Shift + I then clicking on the ‘network’ tab.
Two (and a half) key takeouts.
– The header is important you can improve SEO & UX by getting it right
– The header is dangerous, make sure it is audited as part of SEO checks.
– If you are looking for a job in SEO – check agencies headers, there maybe an advert