# Why Tokenizers Must Treat Special Tags Carefully

Special tags (like `<|endoftext|>`, `[CLS]`, `<s>`, `[SEP]`, or chat template markers) require careful handling for several key reasons:

## 1. They Must Be Atomic
Special tokens should be recognized as **single, indivisible units** rather than being split into subwords or characters. If `<|endoftext|>` gets tokenized as `<`, `|`, `end`, `of`, `text`, `|`, the model loses the special semantic meaning attached to that token.

## 2. Preventing