To generate a piece of writing that is under 500 words in English, you could say:
"I need to write an article that is less than 500 words."
Or more specifically:
"Could you help me generate a 500-word or shorter article?"
If you want someone else to do it for you, you might say:
"Can you help me generate a 500-word or shorter article?"
Would you like me to help you with generating such an article on a specific topic?