Most teams default to WebSockets without question. Here is a clear breakdown of when Server-Sent Events are simpler, cheaper, and more scalable — with concrete SaaS examples to guide your decision.

WebSockets vs. Server-Sent Events: Choosing the Right Real-Time Protocol

Pick any real-time feature tutorial written in the last five years and it almost certainly reaches for WebSockets within the first ten lines. That reflex is understandable — WebSockets are powerful, well-supported, and feel like the "serious" choice. But defaulting to a full-duplex persistent connection when your use case only needs data flowing in one direction is like running a water main to a house that only ever needs a garden hose. It works, but the overhead is unnecessary.

Server-Sent Events (SSE) exist precisely for that garden-hose scenario, and most backend architects underuse them.

What Each Protocol Actually Does

Before comparing trade-offs, a precise definition matters.

WebSockets establish a persistent, bidirectional TCP connection between client and server. Either side can send messages at any time. The handshake upgrades an HTTP connection once, and from that point the channel is open until explicitly closed.

Server-Sent Events use a long-lived HTTP response. The server streams text events to the client over a standard HTTP/1.1 or HTTP/2 connection. The client cannot send data back over that same channel — it uses separate HTTP requests for that. The browser's EventSource API handles reconnection automatically.

// SSE client — three lines is all it takes
const feed = new EventSource('/api/notifications');
feed.onmessage = (e) => renderNotification(JSON.parse(e.data));
feed.onerror   = () => console.warn('SSE reconnecting...');

That is the entire client-side implementation for a notification feed. No library, no handshake logic, no binary framing.

The Axis That Actually Matters: Data Flow Direction

The single most useful question to ask when choosing between these two protocols is: does the client need to send data back over the same persistent connection, or does it only need to receive it?

If the answer is "only receive," SSE is almost certainly the right tool.

Real-world SaaS scenarios where the data flow is server-to-client only:

Live dashboards — analytics platforms pushing updated metric charts every few seconds.
Notification feeds — a project management tool alerting users to new comments or status changes.
Progress indicators — a document export or ML inference job streaming its completion percentage.
Activity logs — a DevOps platform tailing deployment logs in real time.
Stock/price tickers — a fintech SaaS broadcasting asset prices to subscribed users.

None of these require the client to push data back through the same channel. A separate REST or GraphQL call handles any user action. SSE handles the stream.

Real-world scenarios that genuinely need WebSockets:

Collaborative editing — Google Docs-style simultaneous edits where the client must push keystrokes and receive remote changes continuously.
Multiplayer games — latency-sensitive bidirectional state sync.
Live chat — messages flow both ways on the same connection.
Shared whiteboards or design tools — cursor positions, strokes, and selections travel in both directions at high frequency.

Infrastructure and Operational Cost

This is where the choice has real money attached to it.

WebSocket connections are stateful. A server must maintain the connection object in memory for every connected client. This creates challenges for horizontal scaling — if a user's WebSocket is pinned to server instance A and that instance goes down, the connection drops. You need sticky sessions, a message broker (Redis Pub/Sub is common), or a managed WebSocket service to route messages correctly across instances.

SSE rides on HTTP. That means:

Load balancers already know how to handle it. No special WebSocket upgrade support required.
HTTP/2 multiplexing means a single TCP connection can carry SSE streams for multiple browser tabs without extra sockets.
Stateless-friendly. You can fan out SSE events through a simple message queue; each server instance just writes to the response stream for clients it currently holds.

For a SaaS product with 10,000 concurrent users reading a live activity feed, SSE on a well-tuned HTTP/2 stack can be meaningfully cheaper to operate than an equivalent WebSocket infrastructure — particularly on managed cloud platforms where persistent WebSocket connections carry higher per-connection costs.

Where SSE Has Real Limitations

SSE is not universally superior for one-way use cases. Know its constraints.

Binary data is awkward. SSE is a text protocol. Sending binary payloads requires Base64 encoding, which adds overhead. WebSockets handle binary frames natively — relevant for audio streaming or binary sensor data.

Browser connection limits. Under HTTP/1.1, browsers cap concurrent connections to the same origin (typically six). Each EventSource consumes one of those slots. HTTP/2 eliminates this problem, but if your deployment cannot guarantee HTTP/2 end-to-end, SSE can exhaust browser connection pools.

No built-in backpressure. A slow client receiving a high-volume SSE stream can buffer aggressively on the server. This needs to be managed at the application layer.

Mobile and certain proxies. Some older corporate proxies and mobile networks buffer streaming HTTP responses before delivering them, breaking the real-time illusion. WebSockets, using their own framing, are less susceptible to this.

A Decision Framework for SaaS Teams

Use this as a starting checklist when evaluating a new real-time feature:

Bidirectional, low-latency, high-frequency? → WebSockets.
Server pushes updates, client reacts with occasional HTTP calls? → SSE.
Need to support legacy infrastructure or strict HTTP-only environments? → SSE wins on compatibility.
Binary payloads or sub-100ms round trips required? → WebSockets.
Scaling cost is a concern and data flow is one-directional? → SSE is very likely cheaper.
Team prefers minimal dependencies and browser-native APIs? → SSE requires no client library.

A notification system, a live reporting dashboard, or an AI inference progress feed — these are SSE use cases that teams routinely over-engineer with WebSocket infrastructure, paying the operational complexity tax for no functional benefit.

Why This Matters for Your Project

Choosing the right real-time protocol is an architectural decision with downstream effects on your infrastructure costs, deployment complexity, and developer velocity. If your SaaS product has features that push data from server to client — and most do — audit whether those features genuinely need full-duplex connections before you wire up a WebSocket server. SSE is a first-class web standard, well-supported across all modern browsers, and often the more maintainable path. Reserve WebSockets for the problems only WebSockets can solve. Your ops team, and your cloud bill, will thank you.