Even just plain text file without any tags is a valid HTML 5 file. You don't need any tags. <html> and <body> are implied. All you'd need is a <pre> tags or <s

Even just plain text file without any tags is a valid HTML 5 file. You don't need any tags. <html> and <body> are implied. All you'd need is a <pre> tags or <style> somewhere if you'd want it rendered not just as one large paragraph. I guess you may need a <!DOCTYPE html>