Server-Sent Events (SSE)

What is SSE?

Server-Sent Events (SSE) is a standard allowing a server to push data to a client significantly simplier than WebSocket.

While WebSocket provides a full-duplex (two-way) channel, SSE provides a simplex (one-way) channel from server to client. This is perfect for scenarios where the client doesn't need to send data back, such as:

Live news feeds

Stock price tickers

System status updates

LLM / ChatGPT-style streaming responses

Under the Hood

SSE operates over standard HTTP. The client requests a URL, and the server keeps the connection open, sending text messages with a specific content type: Content-Type: text/event-stream.

Code Example: The Message Format

The "stream" consists of plain text blocks separated by newlines.

Server Response:

event: Optional. Allows the client to listen for specific event types.

data: The payload.

id: Optional ID for rescheduling lost messages.

Comparisons: SSE vs. WebSocket

Feature	SSE	WebSocket
Direction	Server-to-Client only	Bi-directional
Protocol	Standard HTTP	Custom TCP Protocol
Complexity	Low (Reconnection is built-in)	High (Requires handshake & heartbeats)
Firewalls	Friendly (Uses port 80/443)	Can be blocked
Binary Data	No (UTF-8 Text only)	Yes

Debugging SSE in Apidog

Apidog treats SSE as a special type of HTTP request.

1. Initiating the Stream

Create a standard HTTP Request.

Enter your endpoint URL.

Send the request.

If the server responds with Content-Type: text/event-stream, Apidog automatically switches to SSE Mode.

2. Timeline View

Instead of waiting for a "final" response (which might never come), Apidog displays a real-time timeline of events as they arrive.

Connections: See when the connection opens and closes.

Events: Each data block is parsed and shown as a discrete message.

Auto-Scroll: Toggle to always see the latest data chunks.

See details SSE

Key Takeaways

Simplex: SSE is a one-way channel from Server to Client, perfect for news feeds, tickers, and AI/LLM responses.

Standard HTTP: Unlike WebSockets, SSE works over standard HTTP/s ports and is firewall-friendly.

Auto-Reconnection: Browsers handle connection drops automatically without extra libraries (unlike raw WebSockets).

Apidog Auto-Detect: Apidog automatically switches to "SSE Mode" when it detects the text/event-stream content type, visualizing the stream in real-time.

Continue with → SOAP

Server-Sent Events (SSE)

What is SSE?#

Under the Hood#

Code Example: The Message Format#

Comparisons: SSE vs. WebSocket#

Debugging SSE in Apidog#

1. Initiating the Stream#

2. Timeline View#

Key Takeaways#