Create a custom format provider C# with Example
public class CustomFormat : IFormatProvider, ICustomFormatter { public string Format(string format, object arg, IFormatProvider formatProvider) { if (!this.Equals(formatProvider)) { return null; } if (format == "Reverse") { return String.Join("", arg.ToString().Reverse()); } return arg.ToString(); } public object GetFormat(Type formatType) { return formatType==typeof(ICustomFormatter) ? this:null; } } Usage: String.Format(new CustomFormat(), "-> {0:Reverse} <-", "Hello World"); Output: -> dlroW olleH <-