WhatsApp uses Erlang for its server-side software.
Erlang was designed at Ericsson for telecommunications systems, where reliability, concurrency, and the ability to keep services running are critical. Those qualities made it a natural fit for a messaging platform that must handle enormous numbers of simultaneous connections and rapidly delivered messages.
WhatsApp’s messaging infrastructure has also used a customized form of XMPP, an open standard for instant messaging and presence information. The company developed FunXMPP to make the protocol more efficient for mobile devices and large-scale messaging. Erlang’s runtime environment helped WhatsApp support fault-tolerant, distributed server processes.
A common mix-up is assuming that Erlang describes every part of the WhatsApp application. Mobile clients also rely on platform-specific technologies for Android, iOS, and desktop operating systems. Erlang is the notable language associated with WhatsApp’s backend and server infrastructure, while the service’s broader technology stack includes protocols, databases, encryption systems, and media-delivery components.