SubGPT is a tool that uses BingGPT to find subdomains based on the ones already discovered for a domain.The tool is free to use and can help in discovering additional subdomains.Installation can be done via pip or by cloning from GitHub, and a Bing cookie is required for the tool to function.Users need to ensure their subdomains list contains subdomains from only one domain and be mindful of Bing's daily limit when using SubGPT.