Friends and I were recently debating the finer points of serving a 410 versus a 404 response code when a brick and mortar retail analogy was born. I hope you'll have half as much fun reading through these amateur comics as I've had putting them together. You might also come away with an extra line of lingo when explaining HTTP Response Codes to clients or colleagues. 

What are Response Codes?

When a search engine or website visitor makes a request to a web server, a three digit HTTP Response Status Code is returned. This code indicates what is about to happen. A response code of 200 means "OK, here is the content you were asking for." A 301 says, "Gotcha. That page has moved, so I'll send you there now." And so on. 

Einstein once said, "If you can't explain it simply, you don't know it well enough." It is in this spirit that I present to you my brick-and-mortar retail store analogy.

A man walks into a store looking for a particular model water gun. In each scenario, he is greeted by a different Sales Associate (our response codes).

200 OK

A 200 is the most common type of response code, and the one we experience most of the time when browsing the web. We asked to see a web page, and it was presented to us without any trouble.

301 Moved Permanently

We were expecting to find a web page in a particular location, but it has been moved. No worries though, the web server has sent us to the new location. Most users won't notice that this has happened unless they watch the URL change.

302 Found (Moved Temporarily)

You're in the right place, but the page has moved temporarily to a new location. Just like a 301 the user doesn't usually notice anything because the web server seemlessly moves them to the new URL.

Important SEO Implication: A 302 isn't a permanent move. Any SEO strength that the original page had won't be granted to the new URL.

401 Unauthorized

We've requested a page, but a username and password are required to access it. We're presented with a way to login. 

Important SEO Implication: Search engines won't submit a username and password for entry. If you have content hidden behind a login, it won't show up in the search results. 

403 Forbidden

We've requested a page that we don't have permission to access at all. This page isn't for us.

404 Not Found

We've requested a page, but the web server doesn't recognize our request. The page can't be shown because the server doesn't know what it is.

Important SEO Implication: Most default 404 pages are a dead end for users and search engines. Look at using a custom 404 for these cases.

410 Gone

We've requested a page and the web server knows what we're asking for, but the page is gone.

Important SEO Implication: There is some debate in the SEO world as to the advantage (if any) of using a 410 over a 404 in certain cases. This post by Barry Schwartz is a good place to start your own research. 

I prefer to use a 410 when removing unfavorable (perhaps penalized) content from a website. Perhaps the website has some bad links pointing to a bad neighborhood within an otherwise quality site. I'd use a 410 to say, "We know what you're asking for, but we've deliberately removed it from the site, permanently."

500 Internal Server Error

We've requested a page, and in return, we get a generic error message. No information is given. It is like looking a sales associate in the eye, asking a question, and recieving a blank stare in return. 

503 Service Unavailable

We asked for a page, but are told that it is temporarily unavailable. Something is wrong. Perhaps the website is down for maintenance.

Status Code Readers & Additional Reading

If you're like me, you came to SEO out of an interest and background in Marketing, rather than approaching it from a start on the Techology side. I understood the meaning of the basic response codes for SEO (301, 302, 404) long before I understood what was technically happening. I needed to see it before I really got it. If you're feeling the same way, you can use a browser plugin to watch the communication between the your browser and a website behind the scenes as you browse the web.

Try these:

• Chrome: HTTP Headers
• Firefox: HttpFox
• Explorer: HTTP Analyzer ($)

There are a number of excellent resources available to help you better understand HTTP Status Codes and determine when to use them to your best advantage for user experience and SEO.

• Here at SEOmoz there is a nice summary and infographic that breaks down the impact on users and search engines in each scenario.
• Ian Lurie placed a solid post on SearchEngineLand that covers .NET and IIS solutions nicely.
• Another way to look at the information is SEOgadget's infographic parralell with London's Tube. Just click the link. You'll see. :)

Happy optimizing!