Understanding GraphQL Subscriptions & How to Simulate Real-Time APIs

Real-time features have become a standard expectation in modern applications—think chat interfaces, dashboards, or live notifications. While these systems make user experiences more dynamic, they also introduce new challenges for developers, especially when it comes to testing. In this post, we’ll explore how GraphQL subscriptions work, why mocking them is difficult, and how you can simulate real-time APIs effectively—even without native GraphQL mocking support.

🧩 What Are GraphQL Subscriptions?

In GraphQL, a subscription allows a client to receive live updates whenever specific data changes on the server. Instead of making repeated requests, the client stays connected through WebSockets or Server-Sent Events (SSE).

subscription OnNewMessage {
  messageAdded {
    id
    text
    user
  }
}

When new data arrives, the server pushes the event to all subscribed clients. It’s elegant in production—but much harder to test in local or automated environments.

⚠️ Why Mocking Subscriptions Is Hard

Mocking GraphQL queries or mutations is simple—you define a request and return a response. Subscriptions, however, are ongoing streams of data, which introduces a few complexities:

• They depend on persistent WebSocket connections
• They require timed events rather than static payloads
• They must handle disconnects, retries, and multiple clients
• The mock must stay in sync with a changing schema

Because of these moving parts, most tool does not offer built-in GraphQL subscription mocking, and MockAPIHub currently focuses on REST API simulation. Still, developers can use MockAPIHub alongside lightweight WebSocket or event simulators to reproduce similar real-time behavior for testing and frontend development.

🧠 Practical Ways to Simulate Real-Time APIs

1. Polling REST Endpoints

A straightforward method is to use regular API calls to simulate real-time updates. You can call a mock endpoint at intervals to mimic a stream of events.

setInterval(async () => {
    const res = await fetch("https://mockapihub.com/api/messages");
    const data = await res.json();
    updateUI(data);
}, 3000);

This pattern gives predictable, controllable test data and works seamlessly with MockAPIHub’s REST mocks.

2. Local WebSocket Servers

If you need a closer simulation of subscriptions, you can spin up a lightweight WebSocket mock.

import { Server } from "mock-socket";
const server = new Server("ws://localhost:8080");

setInterval(() => {
server.emit("message", { text: "Hello from mock server" });
}, 5000);

Your frontend can connect to this local server as if it were a live GraphQL subscription endpoint.

3. Combine WebSockets with REST Mocks

For larger projects, a hybrid setup works best. You can serve static or dynamic REST data from MockAPIHub while emitting real-time updates through a local socket layer.

[Frontend App] → [MockAPIHub REST mocks] → [Local WebSocket Server] → UI updates

This design keeps your test environment lightweight and avoids dependency on real backend services.

🔭 Looking Ahead

Mocking live data streams will always be a challenge, but tools like MockAPIHub make testing predictable and fast. While GraphQL subscription mocks aren’t available yet, we’re exploring flexible solutions for developers who rely on real-time APIs in their workflow.

If you’d like to see GraphQL mocking support added, we’d love your feedback—reach out or share your ideas with the team Here.

🏁 Conclusion

GraphQL subscriptions bring real-time power to web apps, but testing them can feel like chasing a moving target. By combining REST mocks, polling, and lightweight socket servers, you can create reliable simulations without the complexity of live systems.

Keep your development workflow smooth—try MockAPIHub.com and start building faster today.