To mark deprecated code in Ruby simply add a comment to the rdoc and call the Kernel#warn method. For example:

class Foo # DEPRECATED: Please use useful instead. def useless warn "[DEPRECATION] `useless` is deprecated. Please use `useful` instead." useful end def useful # ... end end

If you’re using Yard instead of rdoc, your doc comment should look like this:

# @deprecated Please use {#useful} instead

Also, don’t forget to remove the deprecated method in some future release.

Source: Ryan McGeary’s answer on stackoverflow.