11 May, Nijmegen, The Netherlands €499 I want to buy a ticket »HTTP status codes, like 404, 301, and 500, might not mean much to a regular visitor, but they are incredibly important for SEO. What are HTTP status codes, and why do you see them? According to the official W3C specs, there are dozens of status codes, many of which you’re unlikely to come across. »451: Unavailable for Legal ReasonsThe 451 HTTP status code shows that the requested content was deleted for legal reasons. Read more: 503: Handling site maintenance correctly for SEO »Working with HTTP status codesHTTP status codes are a big part of the lives of SEOs and that of search engine spiders.