MCP NodeJS Debugger

Instructions

Implementation Reference

• src/mcp-server.js:1014-1082 (handler)

  The handler function for the 'get_location' tool. It checks if the debugger is paused, retrieves the current call frame location, builds the call stack, fetches surrounding source code for context, and returns this information as JSON.

    async () => {
      try {
        // Ensure debugger is enabled
        if (!inspector.debuggerEnabled) {
          await inspector.enableDebugger();
        }
        
        if (!inspector.paused || inspector.currentCallFrames.length === 0) {
          return {
            content: [{
              type: "text",
              text: "Debugger is not paused at a breakpoint"
            }]
          };
        }
        
        const frame = inspector.currentCallFrames[0];
        const { url, lineNumber, columnNumber } = frame.location;
        
        // Get call stack
        const callstack = inspector.currentCallFrames.map(frame => {
          return {
            functionName: frame.functionName || '(anonymous)',
            url: frame.url,
            lineNumber: frame.location.lineNumber + 1,
            columnNumber: frame.location.columnNumber
          };
        });
        
        // Get source code for context
        let sourceContext = '';
        try {
          const scriptSource = await inspector.getScriptSource(frame.location.scriptId);
          if (scriptSource) {
            const lines = scriptSource.split('\n');
            const startLine = Math.max(0, lineNumber - 3);
            const endLine = Math.min(lines.length - 1, lineNumber + 3);
            
            for (let i = startLine; i <= endLine; i++) {
              const prefix = i === lineNumber ? '> ' : '  ';
              sourceContext += `${prefix}${i + 1}: ${lines[i]}\n`;
            }
          }
        } catch (err) {
          sourceContext = 'Unable to retrieve source code';
        }
        
        return {
          content: [{
            type: "text",
            text: JSON.stringify({
              url,
              lineNumber: lineNumber + 1,
              columnNumber,
              callstack,
              sourceContext
            }, null, 2)
          }]
        };
      } catch (err) {
        return {
          content: [{
            type: "text",
            text: `Error getting location: ${err.message}`
          }]
        };
      }
    }
  );

• src/mcp-server.js:1010-1083 (registration)

  Registration of the 'get_location' tool with server.tool, including name, description, empty input schema, and inline handler function.

  server.tool(
    "get_location",
    "Gets the current execution location when paused",
    {},
    async () => {
      try {
        // Ensure debugger is enabled
        if (!inspector.debuggerEnabled) {
          await inspector.enableDebugger();
        }
        
        if (!inspector.paused || inspector.currentCallFrames.length === 0) {
          return {
            content: [{
              type: "text",
              text: "Debugger is not paused at a breakpoint"
            }]
          };
        }
        
        const frame = inspector.currentCallFrames[0];
        const { url, lineNumber, columnNumber } = frame.location;
        
        // Get call stack
        const callstack = inspector.currentCallFrames.map(frame => {
          return {
            functionName: frame.functionName || '(anonymous)',
            url: frame.url,
            lineNumber: frame.location.lineNumber + 1,
            columnNumber: frame.location.columnNumber
          };
        });
        
        // Get source code for context
        let sourceContext = '';
        try {
          const scriptSource = await inspector.getScriptSource(frame.location.scriptId);
          if (scriptSource) {
            const lines = scriptSource.split('\n');
            const startLine = Math.max(0, lineNumber - 3);
            const endLine = Math.min(lines.length - 1, lineNumber + 3);
            
            for (let i = startLine; i <= endLine; i++) {
              const prefix = i === lineNumber ? '> ' : '  ';
              sourceContext += `${prefix}${i + 1}: ${lines[i]}\n`;
            }
          }
        } catch (err) {
          sourceContext = 'Unable to retrieve source code';
        }
        
        return {
          content: [{
            type: "text",
            text: JSON.stringify({
              url,
              lineNumber: lineNumber + 1,
              columnNumber,
              callstack,
              sourceContext
            }, null, 2)
          }]
        };
      } catch (err) {
        return {
          content: [{
            type: "text",
            text: `Error getting location: ${err.message}`
          }]
        };
      }
    }
  );

• src/mcp-server.js:1013-1013 (schema)

  Empty input schema for the 'get_location' tool (no parameters required).

  {},