jekyll check_links task. (via. https://github.com/krisb/jekyll-template/blob/master/Rakefile)

Rakefile

desc 'Check links for site already running on localhost:4000'
task :check_links do
  begin
    require 'anemone'
    root = 'http://localhost:4000/'
    Anemone.crawl(root, :discard_page_bodies => true) do |anemone|
      anemone.after_crawl do |pagestore|
        broken_links = Hash.new { |h, k| h[k] = [] }
        pagestore.each_value do |page|
          if page.code != 200
            referrers = pagestore.pages_linking_to(page.url)
            referrers.each do |referrer|
              broken_links[referrer] << page
            end
          end
        end
        broken_links.each do |referrer, pages|
          puts "#{referrer.url} contains the following broken links:"
          pages.each do |page|
            puts "  HTTP #{page.code} #{page.url}"
          end
        end
      end
    end

  rescue LoadError
    abort 'Install anemone gem: gem install anemone'
  end
end