MCP-Hub-MCP Server

Instructions

Implementation Reference

• src/index.ts:91-121 (handler)

  Handler function that executes the 'call-tool' logic: parses arguments, calls serverManager.callTool on the specified server and tool, and returns the result as JSON or an error message.

  async (args, extra) => {
    try {
      const { serverName, toolName, toolArgs } = args;
      const result = await serverManager.callTool(
        serverName,
        toolName,
        toolArgs
      );
  
      return {
        content: [
          {
            type: "text",
            text: JSON.stringify(result, null, 2),
          },
        ],
      };
    } catch (error) {
      return {
        content: [
          {
            type: "text",
            text: `Tool call failed: ${
              (error as Error).message
            }`,
          },
        ],
        isError: true,
      };
    }
  }

• src/types.ts:27-35 (schema)

  Zod schema defining the input parameters for the 'call-tool' tool: serverName (string), toolName (string), toolArgs (record of unknown).

  export const CallToolParamsSchema = z.object({
    serverName: z
      .string()
      .describe("Name of the MCP server to call tool from"),
    toolName: z.string().describe("Name of the tool to call"),
    toolArgs: z
      .record(z.unknown())
      .describe("Arguments to pass to the tool"),
  });

• src/index.ts:83-122 (registration)

  Registration of the 'call-tool' tool on the MCP server using server.tool(), specifying name, description, schema (referencing CallToolParamsSchema), and handler function.

  server.tool(
    "call-tool",
    "Call a specific tool from a specific server",
    {
      serverName: CallToolParamsSchema.shape.serverName,
      toolName: CallToolParamsSchema.shape.toolName,
      toolArgs: CallToolParamsSchema.shape.toolArgs,
    },
    async (args, extra) => {
      try {
        const { serverName, toolName, toolArgs } = args;
        const result = await serverManager.callTool(
          serverName,
          toolName,
          toolArgs
        );
  
        return {
          content: [
            {
              type: "text",
              text: JSON.stringify(result, null, 2),
            },
          ],
        };
      } catch (error) {
        return {
          content: [
            {
              type: "text",
              text: `Tool call failed: ${
                (error as Error).message
              }`,
            },
          ],
          isError: true,
        };
      }
    }
  );

• src/server-manager.ts:205-215 (helper)

  Supporting method in McpServerManager that proxies the tool call to the underlying MCP Client instance for the given server.

  async callTool(
    serverName: string,
    toolName: string,
    args: Record<string, unknown>
  ): Promise<any> {
    const client = this.getClient(serverName);
    return await client.callTool({
      name: toolName,
      arguments: args,
    });
  }