Choosing Real-Time Protocols: WebSockets, SSE, or gRPC?

When building modern applications that need server-to-client updates, you’re faced with a decision: WebSockets, Server-Sent Events (SSE), or gRPC? Each has its advocates, and the internet is full of strong opinions. But like most architectural decisions, the answer is “it depends.”

After working with all three in production, I’ve found that the decision is less about which technology is “best” and more about matching the protocol to your specific constraints. Let’s break this down systematically.

The Three Contenders

Before diving into trade-offs, let’s establish what we’re comparing:

WebSockets provide full-duplex, bidirectional communication over a persistent TCP connection. Think of it as a phone call—both sides can talk whenever they want.

Server-Sent Events (SSE) offer unidirectional, server-to-client communication over HTTP. It’s like a radio broadcast—the server talks, clients listen.

gRPC is Google’s RPC framework built on HTTP/2, using Protocol Buffers for efficient binary serialization. It’s designed for high-performance, polyglot service-to-service communication.

The Mental Model That Matters

Here’s the insight that cuts through most of the complexity: Start by asking whether you need bidirectional communication.

If you only need server-to-client updates (notifications, live feeds, monitoring dashboards), SSE is almost always the right answer. It’s the simplest solution that works, leverages standard HTTP infrastructure, and the browser handles reconnection automatically.

If you need bidirectional communication (chat, collaborative editing, gaming), you’re choosing between WebSockets and gRPC. WebSockets are the well-understood middle ground. gRPC offers better performance but at significant complexity cost.

The Maintainability Trap

This is where many teams get burned: gRPC looks amazing on paper. Binary protocol! Type safety! Code generation! But then you hit the reality:

# Your development workflow becomes:
1. Update .proto file
2. Run protoc compiler
3. Generate code for TypeScript
4. Generate code for Python
5. Generate code for Swift
6. Commit generated code or add build step
7. Hope your teammates' environments work

Compare this to SSE:

// Client
const evtSource = new EventSource('/api/events');
evtSource.addEventListener('notification', (e) => {
    const data = JSON.parse(e.data);
    updateUI(data);
});

// Server
async function* event_generator():
    while True:
        notification = await get_next_notification()
        yield {"event": "notification", "data": notification.json()}

No compilation, no code generation, no toolchain complexity. Just HTTP and JSON. When you’re debugging at 2am, you’ll appreciate being able to curl your endpoint and see plain text responses.

The Scalability Question

“But won’t SSE limit my scalability?” This is the wrong question. The right question is: What scale do you actually need?

For most applications (< 10K concurrent connections), connection overhead is not your bottleneck. Your database queries, serialization logic, and business logic dominate. Any of these protocols work fine.

At medium scale (10K-100K), you need pub/sub infrastructure (Redis, NATS) regardless of protocol choice. SSE, WebSockets, and gRPC all face the same challenge: coordinating state across multiple server instances.

Client → Load Balancer → Server 1 ─┐
                      → Server 2 ─┼→ Redis Pub/Sub → Database
                      → Server 3 ─┘

Only at large scale (100K+ connections) does gRPC’s efficiency become a deciding factor. But at that scale, you’re likely using specialized infrastructure (Pusher, Ably, AWS IoT) anyway.

The Hidden Reliability Win of SSE

Here’s something that surprised me: SSE has better reliability characteristics than WebSockets for many use cases.

The EventSource API automatically reconnects with exponential backoff and sends a Last-Event-ID header to resume from the last received message. This is built into the browser.

With WebSockets, you implement this yourself:

// You're writing this boilerplate for every WebSocket app
let reconnectAttempts = 0;
const ws = new WebSocket('wss://api.example.com');

ws.onclose = () => {
    const delay = Math.min(1000 * Math.pow(2, reconnectAttempts), 30000);
    setTimeout(() => {
        reconnectAttempts++;
        reconnect();
    }, delay);
};

ws.onopen = () => {
    reconnectAttempts = 0;
};

This isn’t just about convenience—it’s about reliability. The browser vendors have spent years tuning reconnection logic, handling edge cases, and optimizing battery life. When you roll your own, you’re unlikely to do better.

The Platform Support Reality

SSE has one significant limitation: no Internet Explorer support. In 2025, this rarely matters, but it’s worth noting.

For mobile apps, the story gets interesting:

  • WebSockets: Excellent native support on iOS and Android
  • SSE: Requires custom implementation (but it’s straightforward)
  • gRPC: Excellent support, official libraries

For web browsers with gRPC, you need gRPC-Web, which requires a proxy to translate between HTTP/1.1 and HTTP/2. This adds deployment complexity.

The Hybrid Approach (Often Best)

In practice, many successful systems use a hybrid approach:

Pattern: REST + SSE

Client actions (POST/PUT/DELETE) → REST API
Server updates → SSE

This gives you:

  • Simple mental model (HTTP for everything)
  • Standard authentication/authorization
  • HTTP caching for actions
  • Real-time updates when needed
  • Easy debugging (everything is text)

This pattern works for activity feeds, notification systems, live dashboards, and progress indicators—probably 80% of real-time use cases.

When Each Protocol Shines

Choose SSE for:

  • Live notifications and activity feeds
  • Real-time dashboards and monitoring
  • Stock tickers and score updates
  • Progress indicators for long operations
  • Any server-to-client-only communication

Choose WebSockets for:

  • Chat applications
  • Collaborative editing
  • Online gaming
  • Trading platforms with bidirectional updates
  • WebRTC signaling

Choose gRPC for:

  • Internal microservices communication
  • Mobile-to-backend (when efficiency is critical)
  • High-throughput systems (millions of messages)
  • Polyglot environments needing strong typing
  • Low-bandwidth scenarios

The Decision Tree

Here’s how I approach this decision:

Do you need bidirectional communication?
│
├─ NO → Are you targeting web browsers?
│   ├─ YES → Use SSE
│   └─ NO → Still use SSE (simple HTTP)
│
└─ YES → Do you have resources for gRPC complexity?
    ├─ YES → Consider gRPC for internal services
    └─ NO → Use WebSockets

The Pragmatic Take

Start simple. Use SSE when server-to-client is enough. Use WebSockets when you need bidirectional. Only reach for gRPC when you have:

  1. Performance requirements that justify the complexity
  2. Team expertise in Protocol Buffers
  3. Infrastructure to support the toolchain
  4. Internal services (not browser-facing)

Most importantly: you can change your mind later. These are implementation details behind your application’s interface. A well-designed system can migrate from SSE to WebSockets or from WebSockets to gRPC without rewriting your entire application.

The best protocol is the simplest one that meets your needs today, not the most impressive one on your resume.

Further Reading