Simple script that tries to load it's arguments as YAML files. Don't forget to chmod +x it.

yml-checker.rb

#!/usr/bin/env ruby
require 'yaml'

files = ARGV

if !files.nil? && files.length >= 1
  files.each do |file|
    if File.exists?(file) && File.file?(file)
      begin
        print "checking #{file}..."
        YAML.load_file file
        puts " looks good"
      rescue Psych::SyntaxError => e
        puts "is invalid!"
        raise e
      rescue
        puts "is not a valid (YAML) file!"
      end
    else
      puts "#{file} does not exists or is not a file"
    end
  end
else
  puts "Usage: #{File.basename(__FILE__)} path/to/yaml/file path/to/another/yaml/file ..."
end