Skip to main content
Notifications enable real-time, one-way communication between clients and servers. They’re used to signal events, state changes, and updates without requiring a response, making them perfect for keeping your application synchronized with server state.

​
Understanding Notifications

MCP notifications are JSON-RPC messages without response requirements. They enable:
  • Real-time updates: Get notified when server state changes
  • List synchronization: Tools, resources, and prompts list updates
  • Custom events: Server-specific notifications for your application
  • Progress tracking: Monitor long-running operations
Bidirectional: Both clients and servers can send notifications. Servers notify clients of changes, while clients notify servers of environment changes like root directories.

​
Notification Flow

Server → Client: Event notifications (tool lists changed, progress updates, custom events) Client → Server: Environment notifications (roots changed, configuration updates)
For information on sending notifications from your MCP server, see the Server Notifications guide.

​
Receiving Notifications (Server → Client)

Register a notification handler on your session using the on method: 
import { MCPClient } from "mcp-use";

const client = new MCPClient({
  mcpServers: {
    myServer: { url: "http://localhost:3000/mcp" }
  }
});

const session = await client.createSession("myServer");

// Register notification handler
session.on("notification", async (notification) => {
  console.log(`Received: ${notification.method}`, notification.params);
});

​
Notification Structure

Notifications follow the JSON-RPC 2.0 format without an id field: 
interface Notification {
  method: string;           // The notification method name
  params?: Record<string, any>;  // Optional parameters
}

​
Standard MCP Notifications

MCP defines several standard notification types that servers may send:

​
Tools List Changed

Sent when the server’s available tools have changed: 
session.on("notification", async (notification) => {
  if (notification.method === "notifications/tools/list_changed") {
    console.log("Tools list updated - refreshing...");
    // Refresh tools cache
    const tools = await session.listTools();
    console.log(`Now have ${tools.length} tools`);
  }
});

​
Resources List Changed

Sent when resources have been added, removed, or modified: 
session.on("notification", async (notification) => {
  if (notification.method === "notifications/resources/list_changed") {
    console.log("Resources updated");
    const resources = await session.listAllResources();
    // Update your UI or cache
  }
});

​
Prompts List Changed

Sent when prompts have changed: 
session.on("notification", async (notification) => {
  if (notification.method === "notifications/prompts/list_changed") {
    console.log("Prompts updated");
    const prompts = await session.listPrompts();
    // Update your UI or cache
  }
});

​
Custom Notifications

Servers can send custom notifications with any method name: 
session.on("notification", async (notification) => {
  switch (notification.method) {
    case "custom/heartbeat":
      console.log(`Heartbeat #${notification.params?.count}`);
      break;
      
    case "custom/user-joined":
      console.log(`User joined: ${notification.params?.username}`);
      break;
      
    case "custom/data-updated":
      console.log("Data updated:", notification.params);
      break;
      
    default:
      console.log(`Unknown notification: ${notification.method}`);
  }
});

​
Sending Notifications (Client → Server)

​
Roots Changed

Roots represent directories or files that the client has access to. When you update roots, the client automatically sends a notifications/roots/list_changed notification to the server: 
import { MCPClient, Root } from "mcp-use";

const client = new MCPClient({
  mcpServers: {
    myServer: { url: "http://localhost:3000/mcp" }
  }
});

const session = await client.createSession("myServer");

// Set roots - this sends notifications/roots/list_changed to the server
await session.setRoots([
  { uri: "file:///home/user/project", name: "My Project" },
  { uri: "file:///home/user/data", name: "Data Directory" }
]);

// Get current roots
const roots = session.getRoots();
console.log(`Current roots: ${roots.length}`);

​
Initial Roots at Connection

You can provide initial roots when creating the connector: 
import { HttpConnector, MCPSession } from "mcp-use";

const connector = new HttpConnector("http://localhost:3000/mcp", {
  roots: [
    { uri: "file:///workspace", name: "Workspace" }
  ]
});

const session = new MCPSession(connector);
await session.connect();
await session.initialize();

// Later, update roots
await session.setRoots([
  { uri: "file:///workspace", name: "Workspace" },
  { uri: "file:///tmp/scratch", name: "Scratch" }
]);

​
TypeScript Types

Import the Notification type for type-safe handlers: 
import { MCPClient, Notification, NotificationHandler } from "mcp-use";

// Type-safe handler
const handler: NotificationHandler = async (notification: Notification) => {
  // notification.method is string
  // notification.params is Record<string, any> | undefined
};

session.on("notification", handler);

​
Root Type

interface Root {
  uri: string;      // Must start with "file://"
  name?: string;    // Optional human-readable name
}

​
Requirements

Notifications require:
  1. Stateful Connection: The server must maintain sessions (stateful mode)
  2. Active Session: The client must have an active, initialized session
  3. Streaming Transport: Either SSE or Streamable HTTP transport
Notifications don’t work in stateless edge environments where sessions aren’t maintained between requests.

​
Next Steps