The world of status codes sounds like a world of incredibly geeky technical jargon – where servers talk in a secret language, spoken only in snidey, sarcastic tones to the technically illiterate when something goes wrong.

To some extent, that’s exactly right.

However, for any website owner, knowing what status codes mean, and what they do, is crucial.

Let’s get the terribly geeky technical summary out the way first: HTTP response status codes are returned by web servers when a browser requests a web page.

When someone enters a specific web page address in their browser, or clicks on a link to view a website, the page will normally just load as expected.

However, sometimes, the page may have expired – moved to a new section as part of a site reshuffle, perhaps. Or maybe the page does exist, but under a different name – so a user may’ve typed when they actually wanted

This is where status codes come in.

There are a range of different status codes, and each has a different function. Most codes are built into websites and are hidden from human users (except when an error, such as the above, has occurred). But crucially, Googlebot reads information about the status of each web page it crawls.

Codes currently in use are numbered in batches from 100 to 500, with the originating number referring to the general status, and subsequent iterations having more specific meanings. For our purposes, 100 to 400 are the relevant ones (the 500 range applies specifically to server errors).

We’ve compiled the most common server return status codes, and we’ll explain how they could affect a potential visitor. We’ll also look at their implications for Google and SEO.

Status Code 100 Range (Provisional Request)

There are only two codes in this status range. Code 100 indicates that the request has been acknowledged; Code 101 indicates that the server needs to switch protocols, but that the request is still proceeding as expected.

Status Code 200 Range (Successful)

Currently used codes are numbered 200 to 206. They are rarely viewed by a web page user as an actual code. Basically, they result in conditions ranging from normal, instantaneous loading, through to a period of load time before the content or web page can be viewed, or it times out.

SEO Implication – Generally, any actual ‘wait time’ is very short. In cases where it becomes extended, it could potentially result in an increased bounce rate, as bored visitors send their clicks elsewhere. There are also some rare cases where pages refuse to load in the time the server defaults to – this anomaly would need some adjustment.

Status Code 300 Range (Redirected)

The 300 range is all about variations in redirection, either permanent or temporary. It is perhaps far more recognisable to most webmasters as a result of the 301 redirect option, which is used deliberately to remove the issues surrounding duplicated web pages resulting from canonicalisation.

For instance, your website is registered on the  domain. A visitor using their browser to find you types A good 301 redirect will ensure the user still arrives at – and they won’t even realise.

Status Code 400 Range (Request Error)

Codes 400 to 417 all indicate that the page cannot be loaded.  Some issues are simply caused by the page requiring the user to authenticate their access by logging in, others are more complex and require the URL in a specific format to allow access.

SEO Implication – Status Code 404 will require particular attention, as it means that incorrect information has been placed in a link, or that an existing link is reaching a ‘dead end’ or ‘bad territory’. Neither is a good thing for visitors, the perception of the website, or from the point of view of Google’s PageRank and indexing policies (which will check you haven’t generated a load of empty or irrelevant URLs, with no relevant content, in order to trick the spiders). It is a serious matter that requires addressing with urgency.

Some sites are really creative with their 404 errors – our own 404 features the ClickThrough rubber duck mascot assuring site users they’re not “quacking up”. Hilarious fun.

In Summary

Although this is fundamental information, available from reputable sources including W3C and the Google Webmaster Tools ‘Help’ pages, many webmasters do not take the trouble to review it.

It is of utmost importance to be aware of what visitors and Googlebot ‘see’ when they attempt to access web pages.

Yes, it sounds geeky, but the premise is simple: don’t settle for avoidable errors.

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About the author:

Alistair Harris is ClickThrough’s head of content. A double-award-winning senior journalist, Ali holds both the NCTJ and NCE qualifications and has more than ten years of experience in traditional press and PR. He has worked in digital marketing and SEO for the past three years and is passionate, enthusiastic and committed to quality.