MCP NodeJS Debugger

Instructions

Implementation Reference

• src/mcp-server.js:482-519 (handler)

  The main handler function for the set_breakpoint tool. Converts the file path to a file URL, escapes it for regex, and sends a Debugger.setBreakpointByUrl command to the inspector with 0-based line number. Stores the breakpoint ID locally and returns success or error message.

  async ({ file, line }) => {
    try {
      // Ensure debugger is enabled
      if (!inspector.debuggerEnabled) {
        await inspector.enableDebugger();
      }
      
      // Convert file path to a URL-like format that the debugger can understand
      // For local files, typically file:///path/to/file.js
      let fileUrl = file;
      if (!file.startsWith('file://') && !file.startsWith('http://') && !file.startsWith('https://')) {
        fileUrl = `file://${file.startsWith('/') ? '' : '/'}${file}`;
      }
      
      const response = await inspector.send('Debugger.setBreakpointByUrl', {
        lineNumber: line - 1, // Chrome DevTools Protocol uses 0-based line numbers
        urlRegex: fileUrl.replace(/[.*+?^${}()|[\]\\]/g, '\\$&'), // Escape special regex characters
        columnNumber: 0
      });
      
      // Store the breakpoint for future reference
      inspector.breakpoints.set(response.breakpointId, { file, line, id: response.breakpointId });
      
      return {
        content: [{
          type: "text",
          text: `Breakpoint set successfully. ID: ${response.breakpointId}`
        }]
      };
    } catch (err) {
      return {
        content: [{
          type: "text",
          text: `Error setting breakpoint: ${err.message}`
        }]
      };
    }
  }

• src/mcp-server.js:479-481 (schema)

  Zod schema defining the input parameters: file (string) and line (number).

    file: z.string().describe("File path where to set breakpoint"),
    line: z.number().describe("Line number for breakpoint")
  },

• src/mcp-server.js:475-482 (registration)

  Registers the set_breakpoint tool with the MCP server using server.tool(), providing name, description, input schema, and handler function.

  server.tool(
    "set_breakpoint",
    "Sets a breakpoint at specified line and file",
    {
      file: z.string().describe("File path where to set breakpoint"),
      line: z.number().describe("Line number for breakpoint")
    },
    async ({ file, line }) => {