Twitch Chat is compatible with IRC, customized as detailed in the documentation. It depends on what you want to do. If you just want to embed chat on your website, you can just use the chat embed. If you want to create a custom Twitch Chat client, you either have you write your own IRC handling (if it’s on a website you’d probably connect via Websockets) or use a library like tmi.js which does a lot of things for you already.