MCP Client

The ai/mcpClient component: v0.36.0+ an MCP (Model Context Protocol) client node that connects to a remote MCP server, invokes the specified tool, and writes the result to the message for downstream nodes. It can also register itself as an MCPToolProvider in the RuleConfig UDF, so agents can call remote tools via ai/agent's self mode.

# Dual Role

The MCP client can be used in two ways inside a rule chain:

Direct invocation: as a rule chain node, calls the specified remote MCP tool on OnMsg
Tool provider: at startup, auto-discovers all tools of the remote MCP server and registers them as an MCPToolProvider for agent MCP tools (server: "self")

# Configuration

Field	Type	Description	Default
server	string	MCP server address. Supports HTTP URLs (`http://`/`https://`) and stdio commands	required
toolName	string	Remote tool name to invoke. Supports `${metadata.xxx}` and `${msg.xxx}` expressions. Empty = taken from `metadata.mcpToolName`
args	string	Tool arguments JSON template. Supports `${msg.xxx}` and `${metadata.xxx}` expressions. Empty = the message body JSON
toolFilter	[]string	Tool filter (affects MCPToolProvider registration only); empty or `["*"]` = register all tools

# Execution Result

The tool result is written to msg.Data and passed downstream via the Success relation
On failure, the error is passed via the Failure relation

# Configuration Examples

# Invoking a Remote Tool Directly

{
  "id": "s1",
  "type": "ai/mcpClient",
  "name": "Get Weather",
  "configuration": {
    "server": "http://localhost:8080/mcp",
    "toolName": "get_weather",
    "args": "{\"city\": \"${msg.city}\", \"unit\": \"celsius\"}"
  }
}

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# Dynamic Tool Name (from Message Metadata)

{
  "id": "s1",
  "type": "ai/mcpClient",
  "name": "MCP Tool Call",
  "configuration": {
    "server": "http://localhost:8080/mcp",
    "toolName": "${metadata.mcpToolName}",
    "args": ""
  }
}

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When toolName is empty, the component reads the tool name from msg.Metadata["mcpToolName"]. When args is empty, the JSON in msg.Data is used as the tool arguments.

# Stdio Mode (Local Process)

{
  "id": "s1",
  "type": "ai/mcpClient",
  "name": "Local MCP Tool",
  "configuration": {
    "server": "mcp-server --port 8080",
    "toolName": "search",
    "args": "{\"query\": \"${msg.query}\"}"
  }
}

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When server is not an HTTP URL, the component parses it as a command line and communicates with the MCP service over stdio.

# As the Agent's Tool Provider

At startup (Start()), the MCP client connects to the remote server, discovers tools, and registers them as an MCPToolProvider. Once configured in a rule chain, agents can use these remote tools in self mode:

{
  "tools": [
    {
      "type": "mcp",
      "config": {
        "server": "self",
        "tools": ["get_weather", "search"]
      }
    }
  ]
}

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toolFilter controls which tools are registered into the MCPToolProvider:

{
  "toolFilter": ["get_weather", "search"]
}

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# Application Example

{
  "ruleChain": {
    "id": "mcp-demo",
    "name": "MCP Invocation Demo",
    "root": true
  },
  "metadata": {
    "firstNodeIndex": 0,
    "nodes": [
      {
        "id": "node_mcp",
        "type": "ai/mcpClient",
        "name": "Call Remote Tool",
        "configuration": {
          "server": "http://localhost:8080/mcp",
          "toolName": "get_weather",
          "args": "{\"city\": \"${msg.city}\"}"
        }
      },
      {
        "id": "node_log",
        "type": "log",
        "name": "Log Result",
        "configuration": {
          "jsScript": "return 'Weather result: ' + msg.data;"
        }
      }
    ],
    "connections": [
      {"fromId": "node_mcp", "toId": "node_log", "type": "Success"}
    ]
  }
}

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Last Updated: 2026/09/11, 05:25:57

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