Use a word counting application to help you write short fiction pieces of precise word length. If you need to write exactly 25, 50, 100, 101, or 499 words, a word count feature like Word or Open Office helps. You could use a web-based word count tool like Word Count Tool, WordCounter, or Grammarly.
What you use is purely personal preference. If you already use one and it works for you, stick with it. If you don’t use one, try out a few and see what works for you.
Just remember, not all word count tools count the same.