How I wish someone would invent one. All you are told is there is a beginning, a middle and an end.
You do need to know the genre – romance, crime, fantasy or horror.
You do need to know who your readers are going to be – young adults, young mothers, middle-aged housewives, business women or the elderly.
You do need to know what type of story a magazine will accept, so you need to research the magazine and download the requirements from the internet.
Now all you need is an idea of what your story is going to be about.
Next you need a plot with problems. Without those no-one will find it interesting.
You now need to write down a biography of your main characters. Without which you will not write with authenticity.
And last of all you need determination and persistence to carry out the task of writing a short story.
But all that will not guarantee success. I wish it did.