MCP NodeJS Debugger

Instructions

Implementation Reference

• src/mcp-server.js:1091-1123 (handler)

  The handler function for the 'get_console_output' tool. It slices the most recent console outputs from inspector.consoleOutput based on the limit, formats them with timestamps and types, and returns them as text content.

  async ({ limit = 20 }) => {
    try {
      if (!inspector.consoleOutput || inspector.consoleOutput.length === 0) {
        return {
          content: [{
            type: "text",
            text: "No console output captured yet"
          }]
        };
      }
  
      // Get the most recent console output entries
      const recentOutput = inspector.consoleOutput.slice(-limit);
      const formattedOutput = recentOutput.map(output => {
        const timestamp = new Date(output.timestamp).toISOString();
        return `[${timestamp}] [${output.type}] ${output.message}`;
      }).join('\n');
  
      return {
        content: [{
          type: "text",
          text: `Console output (most recent ${recentOutput.length} entries):\n\n${formattedOutput}`
        }]
      };
    } catch (err) {
      return {
        content: [{
          type: "text",
          text: `Error getting console output: ${err.message}`
        }]
      };
    }
  }

• src/mcp-server.js:1088-1090 (schema)

  Zod schema defining the optional 'limit' input parameter for the number of recent console entries to retrieve.

  {
    limit: z.number().optional().describe("Maximum number of console entries to return. Defaults to 20")
  },

• src/mcp-server.js:1085-1124 (registration)

  Registration of the 'get_console_output' tool using server.tool(), including name, description, schema, and handler function.

  server.tool(
    "get_console_output",
    "Gets the most recent console output from the debugged process",
    {
      limit: z.number().optional().describe("Maximum number of console entries to return. Defaults to 20")
    },
    async ({ limit = 20 }) => {
      try {
        if (!inspector.consoleOutput || inspector.consoleOutput.length === 0) {
          return {
            content: [{
              type: "text",
              text: "No console output captured yet"
            }]
          };
        }
  
        // Get the most recent console output entries
        const recentOutput = inspector.consoleOutput.slice(-limit);
        const formattedOutput = recentOutput.map(output => {
          const timestamp = new Date(output.timestamp).toISOString();
          return `[${timestamp}] [${output.type}] ${output.message}`;
        }).join('\n');
  
        return {
          content: [{
            type: "text",
            text: `Console output (most recent ${recentOutput.length} entries):\n\n${formattedOutput}`
          }]
        };
      } catch (err) {
        return {
          content: [{
            type: "text",
            text: `Error getting console output: ${err.message}`
          }]
        };
      }
    }
  );

• src/mcp-server.js:174-209 (helper)

  Part of Inspector.handleEvent method that captures 'Runtime.consoleAPICalled' events, processes arguments into a message string, and stores them in this.consoleOutput array (global as inspector.consoleOutput), which is used by the tool.

  case 'Runtime.consoleAPICalled':
  	// Handle console logs from the debugged program
  	const args = event.params.args.map(arg => {
  		if (arg.type === 'string') return arg.value;
  		if (arg.type === 'number') return arg.value;
  		if (arg.type === 'boolean') return arg.value;
  		if (arg.type === 'object') {
  			if (arg.value) {
  				return JSON.stringify(arg.value, null, 2);
  			} else if (arg.objectId) {
  				// We'll try to get properties later as we can't do async here
  				return arg.description || `[${arg.subtype || arg.type}]`;
  			} else {
  				return arg.description || `[${arg.subtype || arg.type}]`;
  			}
  		}
  		return JSON.stringify(arg);
  	}).join(' ');
  	
  	// Store console logs to make them available to the MCP tools
  	if (!this.consoleOutput) {
  		this.consoleOutput = [];
  	}
  	this.consoleOutput.push({
  		type: event.params.type,
  		message: args,
  		timestamp: Date.now(),
  		raw: event.params.args
  	});
  	
  	// Keep only the last 100 console messages to avoid memory issues
  	if (this.consoleOutput.length > 100) {
  		this.consoleOutput.shift();
  	}
  	
  	break;

• src/mcp-server.js:328-329 (helper)

  Initialization of the consoleOutput array on the inspector instance, providing the storage for captured console messages.

  // Initialize console output storage
  inspector.consoleOutput = [];