GPTDuck is an AI-powered tool designed to assist users in understanding and learning codebases. By allowing users to input a GitHub repository, the tool generates answers to questions regarding the repository's structure, functions, and more. This simplifies the process of navigating complex projects, making it easier for developers and professionals to quickly grasp how a particular repo works. It's ideal for those who need to get up to speed with new codebases or troubleshoot existing ones.