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MCP Client

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Overview

This node acts as a client interface to an MCP (Model Context Protocol) server, allowing users to interact with various resources, tools, and prompts provided by the MCP ecosystem. It supports two connection types: Command Line (STDIO) and Server-Sent Events (SSE), enabling flexible communication methods depending on the environment.

Common scenarios where this node is beneficial include:

  • Listing available AI tools or resources from an MCP server.
  • Executing specific AI tools with custom parameters.
  • Retrieving prompt templates for use in workflows.
  • Reading detailed information about specific resources by URI.

Practical examples:

  • Automating the execution of an AI tool that processes text or data within an n8n workflow.
  • Fetching and using prompt templates dynamically to generate content.
  • Monitoring available resources and tools on an MCP server to adapt workflow logic accordingly.

Properties

Name Meaning
Connection Type Choose the transport type to connect to MCP server. Options: "Command Line (STDIO)", "Server-Sent Events (SSE)"
Operation The action to perform on the MCP server. Options include: Execute Tool, Get Prompt, List Prompts, List Resource Templates, List Resources, List Tools, Read Resource
Resource URI URI of the resource to read (required only when Operation is "Read Resource")
Tool Name Name of the tool to execute (required only when Operation is "Execute Tool")
Tool Parameters JSON object containing parameters to pass to the tool (required only when Operation is "Execute Tool")
Prompt Name Name of the prompt template to get (required only when Operation is "Get Prompt")

Output

The output structure varies depending on the selected operation:

  • List Resources: Outputs a JSON object with a resources array listing available resources.
  • List Resource Templates: Outputs a JSON object with a resourceTemplates array.
  • Read Resource: Outputs a JSON object with a resource field containing the resource details.
  • List Tools: Outputs a JSON object with a tools array, each including name, description, and input schema.
  • Execute Tool: Outputs a JSON object with a result field containing the execution result of the specified tool.
  • List Prompts: Outputs a JSON object with a prompts array listing available prompt templates.
  • Get Prompt: Outputs a JSON object with a prompt field containing the requested prompt template.

The node does not output binary data; all outputs are JSON structured.

Dependencies

  • Requires access to an MCP server endpoint.
  • Supports two connection methods:
    • Command Line (STDIO): Requires a command-line executable and optional arguments configured via credentials.
    • Server-Sent Events (SSE): Requires SSE URL and optionally a POST endpoint and headers configured via credentials.
  • Requires appropriate API authentication tokens or credentials depending on the chosen connection type.
  • Environment variables prefixed with MCP_ can be used to set additional environment variables for the command line transport.

Troubleshooting

  • Connection errors: If the node fails to connect to the MCP server, verify that the correct connection type is selected and that credentials (API keys, URLs, commands) are properly configured.
  • Invalid tool parameters: When executing a tool, ensure that the Tool Parameters property contains valid JSON representing an object. Errors parsing JSON will cause failures.
  • Tool not found: If the specified tool name does not exist on the MCP server, the node will throw an error listing available tools.
  • Unsupported operation: Selecting an operation not supported by the node will result in an error.
  • Transport errors: Errors during communication with the MCP server (e.g., network issues, invalid headers) will cause the node to fail with descriptive messages.
  • Environment variable issues: For command line transport, ensure that environment variables required by the MCP client command are correctly set, especially those starting with MCP_.

Links and References

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