r/MachineLearning June 28, 2026 · Communities

I shrank a transformer until every number fitted on the screen and made the weights editable [R]

I've been teaching myself how LLMs actually work, not at the API level, but down to the matrix multiplications. To force myself to really understand the forward pass, I first built a complete transformer by hand in a spreadsheet from embeddings through to the loss. Then I turned the forward pass into a web page so it's