Roots

MCP roots allow clients to inform servers about the relevant locations in the filesystem or other hierarchical data sources. Roots are a client-provided feature—the client declares its root URIs during initialization, and the server can request them to understand the working context.

Overview

Roots provide a mechanism for the client to tell the server which directories, projects, or repositories are relevant to the current session. A server might use roots to:

• Scope file searches to the user's project directories
• Understand which repositories are being worked on
• Limit operations to specific filesystem boundaries

Each root is represented by a Root with a URI and an optional human-readable name.

Declaring roots capability on the client

Clients advertise their support for roots in the capabilities sent during initialization. The roots capability is created automatically when a roots handler is provided. Configure the handler through RootsHandler:

var options = new McpClientOptions
{
    Handlers = new McpClientHandlers
    {
        RootsHandler = (request, cancellationToken) =>
        {
            return ValueTask.FromResult(new ListRootsResult
            {
                Roots =
                [
                    new Root
                    {
                        Uri = "file:///home/user/projects/my-app",
                        Name = "My Application"
                    },
                    new Root
                    {
                        Uri = "file:///home/user/projects/shared-lib",
                        Name = "Shared Library"
                    }
                ]
            });
        }
    }
};

await using var client = await McpClient.CreateAsync(transport, options);

Requesting roots from the server

Servers can request the client's root list using RequestRootsAsync:

[McpServerTool, Description("Lists the user's project roots")]
public static async Task<string> ListProjectRoots(McpServer server, CancellationToken cancellationToken)
{
    var result = await server.RequestRootsAsync(new ListRootsRequestParams(), cancellationToken);

    var summary = new StringBuilder();
    foreach (var root in result.Roots)
    {
        summary.AppendLine($"- {root.Name ?? root.Uri}: {root.Uri}");
    }

    return summary.ToString();
}

Roots change notifications

When the set of roots changes (for example, the user opens a new project), the client notifies the server so it can update its understanding of the working context.

Sending change notifications from the client

Roots change notifications are automatically sent when the client's roots handler is updated. However, clients can also send the notification explicitly:

await mcpClient.SendNotificationAsync(
    NotificationMethods.RootsListChangedNotification,
    new RootsListChangedNotificationParams());

Handling change notifications on the server

Servers can register a handler to respond when the client's roots change:

server.RegisterNotificationHandler(
    NotificationMethods.RootsListChangedNotification,
    async (notification, cancellationToken) =>
    {
        // Re-request the roots list to get the updated set
        var result = await server.RequestRootsAsync(new ListRootsRequestParams(), cancellationToken);
        Console.WriteLine($"Roots updated. {result.Roots.Count} roots available.");
    });