A client is a computer or software that accesses a server and retrieves special services or data from it. It is the task of the client to standardize requests, transmit them to the server, and process the data obtained so that it can be displayed on an output device such as a screen. A client does not execute server tasks, but is merely an intermediate element. Typical clients are web browsers or email clients.

Development and how it works[edit]

Since the 1960s, clients serve the purpose of enabling communication between hardware and servers. One of the oldest protocols is the Telnet protocol. Even today clients work in a similar fashion. The client sends a request to a server or multiple servers and receives data that it interprets and outputs it in a readable form to a user. The client must use a specific protocol to communicate with the server.

In order for the data to be available for other applications, two different data caching options exist, either on the server or client side. A widely used option to store user data on the client are cookies.


The following clients are currently frequently used:

  • Operating systems: server access via the command line using the Telnet protocol
  • Web browser: Communication between server and browser take place via the HTTP protocol. The browser finally evaluates the received HTML documents or JavaScript applications.
  • E-mail clients: Even retrieving emails from a server is done with a client function. Common protocols are POP3, SMTP or IMAP.
  • MMPORG: In online role playing games, the installed software acts as a client, which retrieves and provides the information necessary for the game from a server.
  • Thin clients: These are used for applications that run only on a server and require minimal hardware. Cloud solutions would be an example of this.
  • DNS clients: These clients work automatically in the background and get the appropriate IP address to a URL from the appropriate DNS server.
  • Web-based applications such as web analytic tools like Google Analytics, working with clients.
  • VPN clients: These clients establish a secure connection between a server and a PC via a VPN (Virtual Private Network).

Rich clients vs. thin clients[edit]

Rich clients use the server as little as possible and perform most of their duties locally. These clients are usually completely modular systems such as development environments. In contrast, thin clients work with as little hardware as possible and try to perform all tasks on the server side.

Relevance to search engine optimization[edit]

When programming websites, their presentation should be tested with different clients, i.e. web browsers, because in many cases there are differences depending on the CMS that affect the usability and consequently often also the number of conversions. The adjustment of websites to the respective clients and testing the display of content on different browsers belongs therefore within the scope of SEO.