Building a Large Language Model from Scratch: A Complete Hands-On Learning Roadmap

Key Information

• Original Author/Maintainer: vleonel-junior
• Source Platform: GitHub
• Original Link: https://github.com/vleonel-junior/Build-a-large-language-model-from-scrach
• Release Time: 2026-06-12

This open-source repository systematically organizes the core content of the book Build a Large Language Model (from Scratch). It covers the complete workflow from understanding the Transformer architecture and coding attention mechanisms to text data processing, providing developers who wish to deeply understand the internal mechanisms of LLMs with followable practice code and detailed notes.

Currently, LLMs have become a hot technology in the AI field, but most developers only call APIs without understanding the internal principles. This "black box" state limits their understanding and optimization of the tool. Just as learning programming requires understanding underlying principles, learning LLMs also needs to start from first principles and build a runnable model by hand to truly master its working mechanism.

Chapter Content

1. Understanding Large Language Models: Start with basic concepts, explain that the essence of LLM is a deep neural network that predicts the next word, and establish a knowledge framework from AI → machine learning → deep learning → LLM.
2. Processing Text Data: Covers preprocessing techniques such as tokenization, vocabulary building, and converting text to numerical sequences, emphasizing that data quality has a decisive impact on model performance.
3. Coding Attention Mechanisms: Deeply explains the principle of self-attention calculation, shows how Query/Key/Value work together through code, and explains the parallel advantages of attention mechanisms and the multi-perspective understanding of multi-head attention.

The repository adopts a progressive design: each chapter builds on the previous one, gradually introducing complex implementations from simple concepts to avoid cognitive overload. At the same time, it uses a dual-track model of code + explanation, not only explaining the function of the code but also the design logic, helping to deeply understand the principles of LLMs.

• AI Beginners: Low-threshold entry, build intuitive understanding by running code without complex mathematical derivations.
• Experienced Developers: Deeply understand the internal mechanisms of Transformers, enhance the depth of understanding when calling APIs.
• Researchers: Use the code implemented from scratch as an experimental foundation, modify components to explore performance changes.

1. Hands-On Practice: Clone the repository to local, run the code chapter by chapter, modify parameters and observe the results.
2. Combine with the Original Book: The repository is study notes, and the original book provides systematic theory; combining the two can mutually confirm each other.
3. Try to Expand: After understanding the basics, add new features (such as different positional encodings) or train on larger datasets.

Significance of Open Source

The repository embodies the spirit of open-source knowledge sharing. The author organized study notes to provide valuable resources for the community, helping developers cross the gap from "users" to "understanders".

Conclusion

LLMs are reshaping the technical world, and understanding their internal principles is the foundation for participating in this transformation. This repository provides a clear and practical learning path for developers. Whether you are a novice or an engineer, building an LLM by hand will be an extremely valuable experience.