I Built a BPE Tokenizer From Scratch in Python And Finally Understand How LLMs Work

📰 Medium · Python

Learn how to build a BPE tokenizer from scratch in Python to understand LLMs like ChatGPT and GPT-4

intermediate Published 28 May 2026
Action Steps
  1. Build a BPE tokenizer from scratch in Python using the Medium article as a guide
  2. Run the tokenizer on a sample text to understand how it works
  3. Configure the tokenizer to handle out-of-vocabulary words and special tokens
  4. Test the tokenizer on a dataset to evaluate its performance
  5. Apply the tokenizer to a real-world NLP task, such as text classification or language translation
Who Needs to Know This

NLP engineers and researchers can benefit from understanding the internals of LLMs, and building a BPE tokenizer is a key step in this process. This knowledge can be applied to improve the performance of LLMs in various applications.

Key Insight

💡 Building a BPE tokenizer from scratch can help you understand the internals of LLMs and improve their performance in various applications

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🤖 Built a BPE tokenizer from scratch in Python to understand how LLMs like ChatGPT work! 💻

Key Takeaways

Learn how to build a BPE tokenizer from scratch in Python to understand LLMs like ChatGPT and GPT-4

Full Article

I built a BPE tokenizer, the same tokenization algorithm used inside ChatGPT, GPT-4, and Qwen3 etc from scratch in plain Python. Continue reading on Medium »
Read full article → ← Back to Reads

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