How LLMs Actually Work
From a single neuron to a working transformer, built from scratch in pure NumPy, in your browser. Free to start, no card.
Curated classes in this course
Neural-net foundations
History, a trainable neuron, an N-gram model, and the RNN the transformer replaced.
Tokens & embeddings
Turn text into vectors: tokenizers, embeddings, similarity, and position.
The Transformer block
Self-attention, causal masking, multi-head, LayerNorm, and the full block.
Training, generation & fine-tuning
Assemble a GPT, learn the loss, sample text, and see how assistants are aligned.
How CodeTrain teaches this
No videos and no multiple-choice quiz at the end. Each lesson is a handful of small steps in a real editor. You type the code yourself, it runs, and the tutor reviews what you actually wrote. It will not hand you the answer, and the step doesn't advance until your code passes. What you get at the end is a record of which steps you wrote unaided, not a completion percentage.
These curated courses are the starting point, not the product
Everything in this catalog is a curated course we wrote by hand. They exist so there is something to start on. What CodeTrain actually does is build a lesson on demand: name any topic you want to understand and it writes one for you on the spot, or paste any public repository and it teaches you that codebase from the code that is really in it. You are not limited to the list below, and most people stop using it within a session or two.