Sub 404 is a tool written in python which is used to check the possibility of subdomain takeover vulnerability and it is fast as it is Asynchronous.
During the recon process, you might get a lot of subdomains(e.g more than 10k). It is not possible to test each manually or with traditional requests or the urllib method as it is very slow. Using Sub 404 you can automate this task in a much faster way. Sub 404 uses aiohttp/asyncio which makes this tool asynchronous and faster.