GPT Prompt Engineer is a tool that uses GPT-4 and GPT-3.5-Turbo to generate and test prompts for specific tasks. It allows users to input a description of the task and test cases, and then generates a variety of prompts. These prompts are tested against the test cases using an ELO rating system, which ranks the prompts based on their performance. The tool also provides optional logging to Weights & Biases for tracking the configurations and results. It is a powerful tool for prompt engineering and finding effective prompts for AI language models.