Server-Sent Events (SSE) is an HTTP-based standard that allows servers to stream real-time text events unidirectionally over a single persistent connection.
Server-Sent Events (SSE) is an open web standard (part of the HTML5 specification) that allows servers to push unidirectional real-time data to clients over a standard HTTP/1.1 or HTTP/2 connection with Content-Type: text/event-stream. Unlike bidirectional WebSockets, SSE utilizes standard HTTP transport, automatically handles reconnection, and is the industry-standard transport for LLM token streaming (OpenAI, Anthropic, Vercel AI SDK).
Test streaming endpoints with the API Request Builder or inspect WebSocket connections in the WebSocket Tester.
| Feature | Server-Sent Events (SSE) | WebSockets |
|---|---|---|
| Directionality | Unidirectional (Server → Client) | Full Duplex (Bidirectional) |
| Protocol | Standard HTTP / HTTPS | Custom ws:// / wss:// TCP protocol |
| Auto Reconnection | Built-in by browser EventSource |
Manual custom reconnection logic required |
| Firewall & Proxy Compatibility | Works over standard HTTP/2 (zero issues) | Can be blocked by corporate HTTP proxies |
| Ideal Use Case | AI token streaming, notifications, live feeds | Real-time gaming, collaborative canvas editing |
Free, browser-based utilities to test, generate, and inspect Server-Sent Events (SSE) & EventSource API payloads directly.
Build and test HTTP API requests with headers, body, auth, and response visualization.
Connect to WebSocket endpoints (ws:// or wss://) in real time to inspect frames, measure latency, test heartbeats, and debug payloads.
Convert cURL commands to idiomatic code across 14 programming languages instantly.
Analyze HTTP response headers for security, caching, and compliance issues.
