HTTP

HTTP is the standard protocol of the web: the browser (client) sends requests to the server, which responds with a status code and content. HTTPS is the encrypted variant and standard today; status codes such as 200, 301 and 404 are central to SEO.

HTTP (Hypertext Transfer Protocol) is the protocol browsers and web servers use to exchange data on the World Wide Web – a defined set of rules for requests and responses. When a user calls up a page by entering a URL or clicking a link, the browser (client) sends a request to the server. The server returns a response: a status code showing whether the request was successful, and the requested content such as HTML, images or scripts. Today, HTTPS, the encrypted variant, is used almost exclusively: it transmits data with TLS encryption so that it can't be read or altered along the way. Browsers mark unencrypted HTTP pages as “not secure”, and Google has treated HTTPS as a ranking signal since 2014. For online shops, where customers enter address and payment details, HTTPS is indispensable anyway.

An example: if a user enters www.example.com/example-text.html, the browser first determines the server's IP address via the Domain Name System (DNS). It then sends a request to deliver the file /example-text.html. If successful, the server responds with status code 200 and the content of the page. Other important status codes are 301 (permanent redirect), 302 (temporary redirect), 404 (page not found), 410 (page permanently removed) and 500 or 503 (server errors). These codes are central to search engine optimisation: they determine whether Google indexes a page, follows a redirect or removes a URL from the index. How quickly a page loads depends on the server, connection and amount of data, among other things. Newer protocol versions such as HTTP/2 and HTTP/3 transfer several files in parallel over one connection, speeding up page loading.

Developed at CERN

Like the World Wide Web as a whole, HTTP was developed at CERN – the European Organization for Nuclear Research near Geneva. From 1989, Tim Berners-Lee and his colleagues designed the foundations of the web: HTTP, the URL as an address and HTML as the markup language. Roy Fielding and others later made major contributions to standardising HTTP/1.1.