Building real-time web or mobile applications requires careful selection of protocols to ensure efficient data delivery between servers and clients. MQTT (Message Queuing Telemetry Transport) and Server-Sent Events (SSE) are two protocols that serve different purposes in this context. MQTT, a bi-directional protocol, is ideal for IoT applications where devices require lightweight communication over unreliable networks, while SSE, a mono-directional protocol, is more suited for applications like real-time news services where information is pushed from the server to the client. MQTT relies on a broker to manage data exchange, supporting resource-constrained devices with its lightweight nature and Quality of Service (QoS) features, though it may have limitations concerning security and scaling. Conversely, SSE uses a simpler client-server model without brokers, synchronizing data over HTTP and offering built-in support for connection re-establishment, though it is limited to UTF-8 encoding and a specific number of open connections. Implementing these protocols in-house can present challenges, such as ensuring security and message delivery, prompting some developers to consider commercial solutions like Ably, which provides infrastructure and APIs for seamless integration of both MQTT and SSE.