Older Rails versions used to use the Quiet Assets GEM which was then rolled directly into the Rails asset pipeline with

# config/environments/development.rb

config.assets.quiet = true

This switch works with Webrick and the development.log file, but I usually code with Webrick and byebug for debugging, so I have the console open and am always reading the STDOUT stream. The Asset logging stream is NOT silenced from the STDOUT so my console is still hopelessly cluttered.

Ruby monkey-patching to the rescue:

if Rails.env.development? && defined?(::WEBrick)
  # Stop all the /assets/ logs in the webrick stdout
  module WEBrick
    class HTTPServer < ::WEBrick::GenericServer
      def access_log(config, req, res)
        # so assets don't log
      end
    end
  end

end