By 2026, FastAPI has become the fastest-growing framework within the Python ecosystem. Its combination of performance, modern typing, and ease of use make it the preferred tool for creating APIs, microservices, and real-time applications with WebSockets.
This guide teaches you what is FastAPI, how to use it with WebSockets and how to build your first reactive application without complications.
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FastAPI is a modern framework for Python based on ASGI and built on Starlette. This makes it perfect for applications that require real-time communication, such as:
– Live chats
– Financial dashboards
– Online games
– IoT monitoring
– Collaborative apps
Thanks to its native support for WebSockets, you can create instantaneous bi-directional communications without getting tangled up in complex configurations.
A WebSocket is a permanent communication channel between client and server. Unlike classic HTTP, here there’s no need to reload or request data again; everything flows continuously.
Key benefits:– Low latency
– Bi-directional communication
– Ideal for real-time applications
– Lower cost than traditional polling
pip install fastapi uvicorn
Step 2: Create a real-time server
Create an file called server.py:
from fastapi import FastAPI, WebSocket from fastapi.responses import HTMLResponse app = FastAPI() @app.websocket("/ws") async def websocket_endpoint(websocket: WebSocket): await websocket.accept() while True: message = await websocket.receive_text() await websocket.send_text(f"Message received: {message}")
This server:– Accepts connections
– Listens for messages
– Responds in real-time
uvicorn server:app --reload
Step 4: Create an HTML client to test it
WebSocket Chat with FastAPI
You now have a real-time communication working.
Add a simple connection manager.
class ConnectionManager: def __init__(self): self.connections = [] async def connect(self, websocket: WebSocket): await websocket.accept() self.connections.append(websocket) async def broadcast(self, message: str): for ws in self.connections: await ws.send_text(message) manager = ConnectionManager() @app.websocket("/ws") async def websocket_endpoint(websocket: WebSocket): await manager.connect(websocket) while True: data = await websocket.receive_text() await manager.broadcast(f"New message: {data}")
NOW any message will be sent to all clients.
– Chats with integrated AI
– IoT control panels
– Mobile apps with Llama running prompts in real-time streaming
– Live trading and alerts
– Push notifications without FCM or APNS
– Lightweight multi-player games
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