What are Server-Sent Events?

Server-Sent Events (SSE) is a standard that allows servers to push data to web clients over HTTP. Unlike WebSockets, SSE is unidirectional - the server sends events to the client.

Basic SSE Format

event: message
data: {"hello": "world"}

data: Just data, no event type

event: custom-event
id: 123
data: With event type and ID

Each event can have:

data: The payload (required)
event: Custom event type (optional, defaults to "message")
id: Event identifier (optional)
retry: Reconnection time in ms (optional)

SSE is widely used for AI streaming responses (OpenAI, Anthropic, Vercel AI SDK), real-time feeds, notifications, and live updates.

Supported Formats

Click "Try this" to see how Beautify Event Stream parses each format.

Standard SSE

The basic Server-Sent Events format as defined by the W3C specification.

event: message
data: {"status":"connected","user":"john_doe"}

event: update
data: {"count":42,"timestamp":"2024-01-15T10:30:00Z"}

event: message
data: {"status":"processing"}

data: Simple text without event type

event: done
data: {"status":"complete"}

Vercel AI SDK

The streaming protocol used by Vercel AI SDK with prefixed message types (0: text, e: error, d: done).

0:"Hello"
0:" there"
0:"!"
0:" How"
0:" can"
0:" I"
0:" help"
0:" you"
0:" today"
0:"?"
e:{"finishReason":"stop","usage":{"promptTokens":10,"completionTokens":15},"isContinued":false}
d:{"finishReason":"stop","usage":{"promptTokens":10,"completionTokens":15}}

OpenAI Streaming

The SSE format used by OpenAI chat completions API with delta chunks.

data: {"id":"chatcmpl-123","object":"chat.completion.chunk","created":1694268190,"model":"gpt-4","choices":[{"index":0,"delta":{"role":"assistant","content":""},"finish_reason":null}]}

data: {"id":"chatcmpl-123","object":"chat.completion.chunk","created":1694268190,"model":"gpt-4","choices":[{"index":0,"delta":{"content":"Hello"},"finish_reason":null}]}

data: {"id":"chatcmpl-123","object":"chat.completion.chunk","created":1694268190,"model":"gpt-4","choices":[{"index":0,"delta":{"content":"!"},"finish_reason":null}]}

data: {"id":"chatcmpl-123","object":"chat.completion.chunk","created":1694268190,"model":"gpt-4","choices":[{"index":0,"delta":{},"finish_reason":"stop"}]}

data: [DONE]

Anthropic Streaming

The SSE format used by Anthropic Claude API with content block deltas.

data: {"type":"message_start","message":{"id":"msg_01","type":"message","role":"assistant","model":"claude-3-opus-20240229"}}

data: {"type":"content_block_start","index":0,"content_block":{"type":"text","text":""}}

data: {"type":"content_block_delta","index":0,"delta":{"type":"text_delta","text":"Hello"}}

data: {"type":"content_block_delta","index":0,"delta":{"type":"text_delta","text":" World"}}

data: {"type":"content_block_delta","index":0,"delta":{"type":"text_delta","text":"!"}}

data: {"type":"content_block_stop","index":0}

data: {"type":"message_stop"}

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