A guide to building a world-class language model from absolute scratch. Taught like you’re five. Built like you’re an engineer. I made this with the goal of learning something I didn’t understand completely. Specifically the attention part. I use AI a lot to understand key concepts and verifying them. This is a 12-chapter, 3,900+ line interactive textbook that teaches you how to build, train and run a modern language model from absolute scratch. The same family of architecture behind ChatGPT, Claude, LLaMA and Mistral. You won’t just read about Transformers. You’ll write every line yourself: tokenizer, embeddings, attention, training loop, inference engine. Every single line annotated to explain what it does and why it’s there.
How to Train Your GPT
