• Microsoft .Net Standard 2.0
  • Microsoft .Net Standard 2.1
  • Microsoft .Net 6.0 (or later)



Ookii.CommandLine is a powerful and flexible command line argument parsing library for .Net applications.

  • Easily define arguments by creating a class with properties.
  • Create applications with multiple subcommands.
  • Generate fully customizable usage help.
  • Supports PowerShell-like and POSIX-like parsing rules.

A C++ version is also available.

Two styles of command line parsing rules are supported: the default mode uses rules similar to those used by PowerShell, and the alternative long/short mode uses a style influenced by POSIX conventions, where arguments have separate long and short names with different prefixes. Many aspects of the parsing rules are configurable.

To determine which arguments are accepted, you create a class, with constructor parameters and properties that define the arguments. Attributes are used to specify names, create required or positional arguments, and to specify descriptions for use in the generated usage help.

For example, the following class defines four arguments: a required positional argument, an optional positional argument, a named-only argument, and a switch argument (sometimes also called a flag):

partial class MyArguments
    [CommandLineArgument(IsPositional = true)]
    [Description("A required positional argument.")]
    public required string Required { get; set; }

    [CommandLineArgument(IsPositional = true)]
    [Description("An optional positional argument.")]
    public int Optional { get; set; } = 42;

    [Description("An argument that can only be supplied by name.")]
    public DateTime Named { get; set; }

    [Description("A switch argument, which doesn't require a value.")]
    public bool Switch { get; set; }

For more information, please see the documentation on GitHub.