MCP File Editor Server

Instructions

Implementation Reference

• src/index.ts:133-166 (handler)

  The main handler function that performs the deletion of lines from the file after validating the path, file existence, and starting line content.

  execute: async ({ file_path, line_start, line_end, line_start_contents }) => {
    const absolutePath = validateAbsolutePath(file_path, 'file_path');
    validateFileExists(absolutePath);
  
    try {
      // Verify the starting line content
      verifyLineContent(absolutePath, line_start, line_start_contents);
  
      const content = fs.readFileSync(absolutePath, 'utf-8');
      const lines = content.split('\n');
  
      if (line_start > lines.length || line_end > lines.length) {
        throw new UserError(`Line range ${line_start}-${line_end} is beyond file length (${lines.length} lines).`);
      }
  
      if (line_start > line_end) {
        throw new UserError('line_start must be less than or equal to line_end.');
      }
  
      // Remove the specified lines (inclusive)
      const newLines = [
        ...lines.slice(0, line_start - 1), // Lines before start
        ...lines.slice(line_end) // Lines after end
      ];
  
      const newContent = newLines.join('\n');
      fs.writeFileSync(absolutePath, newContent, 'utf-8');
  
      return `Successfully deleted lines ${line_start}-${line_end} from "${absolutePath}".`;
    } catch (error: any) {
      if (error instanceof UserError) throw error;
      throw new UserError(`Error deleting content from file "${absolutePath}": ${error.message}`);
    }
  }

• src/index.ts:127-132 (schema)

  Zod schema defining the input parameters for the delete_from_file tool.

  parameters: z.object({
    file_path: z.string().describe('Absolute path to the file'),
    line_start: z.number().int().positive().describe('Starting line number (1-based)'),
    line_end: z.number().int().positive().describe('Ending line number (1-based)'),
    line_start_contents: z.string().describe('Expected content of the starting line (used for verification)')
  }),

• src/index.ts:124-167 (registration)

  Registration of the delete_from_file tool using server.addTool.

  server.addTool({
    name: 'delete_from_file',
    description: 'Delete content from a file between specified line numbers.',
    parameters: z.object({
      file_path: z.string().describe('Absolute path to the file'),
      line_start: z.number().int().positive().describe('Starting line number (1-based)'),
      line_end: z.number().int().positive().describe('Ending line number (1-based)'),
      line_start_contents: z.string().describe('Expected content of the starting line (used for verification)')
    }),
    execute: async ({ file_path, line_start, line_end, line_start_contents }) => {
      const absolutePath = validateAbsolutePath(file_path, 'file_path');
      validateFileExists(absolutePath);
  
      try {
        // Verify the starting line content
        verifyLineContent(absolutePath, line_start, line_start_contents);
  
        const content = fs.readFileSync(absolutePath, 'utf-8');
        const lines = content.split('\n');
  
        if (line_start > lines.length || line_end > lines.length) {
          throw new UserError(`Line range ${line_start}-${line_end} is beyond file length (${lines.length} lines).`);
        }
  
        if (line_start > line_end) {
          throw new UserError('line_start must be less than or equal to line_end.');
        }
  
        // Remove the specified lines (inclusive)
        const newLines = [
          ...lines.slice(0, line_start - 1), // Lines before start
          ...lines.slice(line_end) // Lines after end
        ];
  
        const newContent = newLines.join('\n');
        fs.writeFileSync(absolutePath, newContent, 'utf-8');
  
        return `Successfully deleted lines ${line_start}-${line_end} from "${absolutePath}".`;
      } catch (error: any) {
        if (error instanceof UserError) throw error;
        throw new UserError(`Error deleting content from file "${absolutePath}": ${error.message}`);
      }
    }
  });

• src/utils.ts:90-124 (helper)

  Helper function to verify the content of the starting line before deletion, ensuring safety and correctness.

  export function verifyLineContent(filePath: string, lineNumber: number, expectedContent: string): string {
    try {
      const content = fs.readFileSync(filePath, 'utf-8');
      const lines = content.split('\n');
  
      if (lineNumber < 1 || lineNumber > lines.length) {
        throw new UserError(
          `Line ${lineNumber} does not exist in file "${filePath}". The file has ${lines.length} lines. ` +
          `Please verify the line number and re-read the file with show_line_numbers=true to see the current content.`
        );
      }
  
      const actualContent = lines[lineNumber - 1]; // Convert to 0-based index
      const normalizedActual = actualContent.trim().replace(/\s+/g, ' ');
      const normalizedExpected = expectedContent.trim().replace(/\s+/g, ' ');
  
      if (normalizedActual !== normalizedExpected) {
        throw new UserError(
          `Line content verification failed for line ${lineNumber} in "${filePath}".\n` +
          `Expected (normalized): "${normalizedExpected}"\n` +
          `Actual (normalized): "${normalizedActual}"\n` +
          `Please re-read the file with show_line_numbers=true to see the current content and update your request accordingly.`
        );
      }
  
      return actualContent;
    } catch (error) {
      if (error instanceof UserError) {
        throw error;
      }
      throw new UserError(
        `Error reading file "${filePath}" for line verification: ${error instanceof Error ? error.message : String(error)}`
      );
    }
  }