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The MCP Inspector provides comprehensive RPC logging capabilities that allow you to monitor all JSON-RPC messages exchanged between the inspector and your MCP servers in real-time. This feature is essential for debugging, understanding server behavior, and troubleshooting connection issues.

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Overview

Detailed view of an expanded RPC message with JSON payload

Expanded RPC message showing detailed JSON payload

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What is RPC Logging?

RPC (Remote Procedure Call) logging captures every JSON-RPC message sent to and received from MCP servers. This includes:
  • Tool calls: Requests to execute tools and their responses
  • Resource requests: Queries for resources and their results
  • Prompt requests: Prompt execution requests and responses
  • Notifications: Server-initiated notifications
  • Errors: Error responses and connection issues

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Opening the RPC Panel

1

Navigate to a Tab

Open the Tools, Resources, or Prompts tab for a connected server.
2

Locate RPC Panel

The RPC Messages panel appears at the bottom of the left sidebar. It starts collapsed by default.
3

Expand Panel

Click on the “RPC Messages” header to expand the panel. You can resize it by dragging the handle above it.
RPC logging interface showing message list

RPC Messages panel showing real-time JSON-RPC message logging

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Understanding the Interface

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Message List

Each RPC message is displayed as a row with:
  • Timestamp: Local time when the message was received
  • Direction Badge:
    • ↑ SEND - Outgoing messages from inspector to server
    • ↓ RECEIVE - Incoming messages from server to inspector
  • Method Name: The JSON-RPC method being called (e.g., tools/call, resources/read)
  • Expandable Content: Click to view the full JSON payload

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Technical Details

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Message Format

Each logged message contains: 
{
  id: string;              // Unique message ID
  serverId: string;        // Server identifier
  direction: "SEND" | "RECEIVE";
  method: string;          // JSON-RPC method name
  timestamp: string;       // ISO timestamp
  payload: unknown;        // Full JSON-RPC payload
}