← Home

Server-Sent Events (SSE) Protocol

This section explains how MCP servers use Server-Sent Events (SSE) for real-time communication, performance monitoring, and streaming capabilities.

What is Server-Sent Events (SSE)?

Server-Sent Events (SSE) is a standard HTTP-based technology that enables servers to push updates to clients over a single, long-lived connection. Unlike WebSockets, SSE is unidirectional (server to client only) and operates over standard HTTP, making it simpler to implement and more compatible with existing infrastructure.

Key Features of SSE

Real-time Data Streaming: Efficient one-way communication from server to client
Built on HTTP: No special protocols or ports required
Automatic Reconnection: Browsers automatically attempt to reconnect if the connection is lost
Event IDs: Support for event tracking and resuming missed events
Event Types: Ability to categorize different types of events
Text-based Format: Simple and human-readable message format

How MCP Servers Use SSE

MCP servers leverage SSE for several critical functions:

Real-time Metrics: Stream performance metrics and resource utilization data
Log Streaming: Provide real-time access to server logs
Stateful Responses: Stream partial responses as they become available
Status Updates: Notify clients of deployment and operational status changes
Progress Indicators: Communicate progress during long-running operations

Introduction - Detailed explanation of SSE concepts
Implementation - How to implement SSE clients and servers
Event Types - Standard event types used in MCP servers
Best Practices - Recommendations for effective SSE usage

Example SSE Flow

Here's a simplified diagram of how SSE works with MCP servers:

Client                                                MCP Server
  │                                                      │
  │  1. HTTP GET /api/servers/{id}/events                │
  │ ─────────────────────────────────────────────────────>
  │                                                      │
  │  2. HTTP 200 OK                                      │
  │  Content-Type: text/event-stream                     │
  │ <─────────────────────────────────────────────────────
  │                                                      │
  │  3. event: metrics                                   │
  │     data: {"cpu": 23, "memory": 128, "requests": 45} │
  │ <─────────────────────────────────────────────────────
  │                                                      │
  │  4. event: log                                       │
  │     data: {"level": "info", "msg": "Request processed"} │
  │ <─────────────────────────────────────────────────────
  │                                                      │
  │                  ... Connection remains open ...     │
  │                                                      │
  │  5. event: status                                    │
  │     data: {"status": "scaling", "instances": 2}      │
  │ <─────────────────────────────────────────────────────
  │                                                      │

Benefits for Integration

Using SSE for integrations with workflow management tools like n8n provides several advantages: