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Documentation Index

Fetch the complete documentation index at: https://modelcontextprotocol.io/llms.txt

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

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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.

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Capabilities

Servers that emit log message notifications MUST declare the logging capability: 
{
  "capabilities": {
    "logging": {}
  }
}

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Log Levels

The protocol follows the standard syslog severity levels specified in RFC 5424:
LevelDescriptionExample Use Case
debugDetailed debugging informationFunction entry/exit points
infoGeneral informational messagesOperation progress updates
noticeNormal but significant eventsConfiguration changes
warningWarning conditionsDeprecated feature usage
errorError conditionsOperation failures
criticalCritical conditionsSystem component failures
alertAction must be taken immediatelyData corruption detected
emergencySystem is unusableComplete system failure

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Requesting Log Messages

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Per-request log level

To receive log messages for a specific request, include io.modelcontextprotocol/logLevel in the request’s _meta. The server MUST NOT emit notifications/message for a request that does not include this field. The server sends notifications/message notifications on the response stream at or above the requested level before the final response.

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Protocol Messages

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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
      }
    }
  }
}

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Error Handling

Servers SHOULD return standard JSON-RPC errors for common failure cases:
  • Invalid log level: -32602 (Invalid params)
  • Internal errors: -32603 (Internal error)

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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

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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