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Client Features

Roots

Protocol Revision: draft
The Model Context Protocol (MCP) provides a standardized way for clients to exposefilesystem “roots” to servers. Roots define the boundaries of where servers can operatewithin the filesystem, allowing them to understand which directories and files they haveaccess to. Servers can request the list of roots from supporting clients and receivenotifications when that list changes.

User Interaction Model

Roots in MCP are typically exposed through workspace or project configuration interfaces.For example, implementations could offer a workspace/project picker that allows users toselect directories and files the server should have access to. This can be combined withautomatic workspace detection from version control systems or project files.However, implementations are free to expose roots through any interface pattern thatsuits their needs—the protocol itself does not mandate any specific userinteraction model.

Capabilities

Clients that support rootsMUST declare theroots capability duringinitialization:
{  "capabilities": {    "roots": {      "listChanged":true    }  }}
listChanged indicates whether the client will emit notifications when the list of rootschanges.

Protocol Messages

Listing Roots

To retrieve roots, servers send aroots/list request:Request:
{  "jsonrpc":"2.0",  "id":1,  "method":"roots/list"}
Response:
{  "jsonrpc":"2.0",  "id":1,  "result": {    "roots": [      {        "uri":"file:///home/user/projects/myproject",        "name":"My Project"      }    ]  }}

Root List Changes

When roots change, clients that supportlistChangedMUST send a notification:
{  "jsonrpc":"2.0",  "method":"notifications/roots/list_changed"}

Message Flow

Data Types

Root

A root definition includes:
  • uri: Unique identifier for the root. ThisMUST be afile:// URI in the currentspecification.
  • name: Optional human-readable name for display purposes.
Example roots for different use cases:

Project Directory

{  "uri":"file:///home/user/projects/myproject",  "name":"My Project"}

Multiple Repositories

[  {    "uri":"file:///home/user/repos/frontend",    "name":"Frontend Repository"  },  {    "uri":"file:///home/user/repos/backend",    "name":"Backend Repository"  }]

Error Handling

ClientsSHOULD return standard JSON-RPC errors for common failure cases:
  • Client does not support roots:-32601 (Method not found)
  • Internal errors:-32603
Example error:
{  "jsonrpc":"2.0",  "id":1,  "error": {    "code":-32601,    "message":"Roots not supported",    "data": {      "reason":"Client does not have roots capability"    }  }}

Security Considerations

  1. ClientsMUST:
    • Only expose roots with appropriate permissions
    • Validate all root URIs to prevent path traversal
    • Implement proper access controls
    • Monitor root accessibility
  2. ServersSHOULD:
    • Handle cases where roots become unavailable
    • Respect root boundaries during operations
    • Validate all paths against provided roots

Implementation Guidelines

  1. ClientsSHOULD:
    • Prompt users for consent before exposing roots to servers
    • Provide clear user interfaces for root management
    • Validate root accessibility before exposing
    • Monitor for root changes
  2. ServersSHOULD:
    • Check for roots capability before usage
    • Handle root list changes gracefully
    • Respect root boundaries in operations
    • Cache root information appropriately

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