Logging ↗

Documentation Index#

Fetch the complete documentation index at: https://modelcontextprotocol.io/llms.txt Use this file to discover all available pages before exploring further.

Protocol Revision: 2025-11-25

The Model Context Protocol (MCP) provides a standardized way for servers to send structured log messages to clients. Clients can control logging verbosity by setting minimum log levels, with servers sending notifications containing severity levels, optional logger names, and arbitrary JSON-serializable data.

User Interaction Model#

Implementations are free to expose logging through any interface pattern that suits their needs—the protocol itself does not mandate any specific user interaction model.

Capabilities#

Servers that emit log message notifications MUST declare the logging capability:

{
  "capabilities": {
    "logging": {}
  }
}

Log Levels#

The protocol follows the standard syslog severity levels specified in RFC 5424:

Protocol Messages#

Setting Log Level#

To configure the minimum log level, clients MAY send a logging/setLevel request:

Request:

{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "logging/setLevel",
  "params": {
    "level": "info"
  }
}

Log Message Notifications#

Servers send log messages using notifications/message notifications:

{
  "jsonrpc": "2.0",
  "method": "notifications/message",
  "params": {
    "level": "error",
    "logger": "database",
    "data": {
      "error": "Connection failed",
      "details": {
        "host": "localhost",
        "port": 5432
      }
    }
  }
}

Message Flow#

sequenceDiagram
    participant Client
    participant Server

    Note over Client,Server: Configure Logging
    Client->>Server: logging/setLevel (info)
    Server-->>Client: Empty Result

    Note over Client,Server: Server Activity
    Server--)Client: notifications/message (info)
    Server--)Client: notifications/message (warning)
    Server--)Client: notifications/message (error)

    Note over Client,Server: Level Change
    Client->>Server: logging/setLevel (error)
    Server-->>Client: Empty Result
    Note over Server: Only sends error level<br/>and above

Error Handling#

Servers SHOULD return standard JSON-RPC errors for common failure cases:

• Invalid log level: -32602 (Invalid params)
• Configuration errors: -32603 (Internal error)

Implementation Considerations#

1. Servers SHOULD:

   • Rate limit log messages
   • Include relevant context in data field
   • Use consistent logger names
   • Remove sensitive information

2. Clients MAY:

   • Present log messages in the UI
   • Implement log filtering/search
   • Display severity visually
   • Persist log messages

Security#

1. Log messages MUST NOT contain:

   • Credentials or secrets
   • Personal identifying information
   • Internal system details that could aid attacks

2. Implementations SHOULD:

   • Rate limit messages
   • Validate all data fields
   • Control log access
   • Monitor for sensitive content