# Special token

> Special token: A vocabulary entry with a control meaning rather than text, such as end-of-text or a chat-role marker. User text must never become one.

Canonical: https://llmdojo.dev/glossary/special-token

Also called special tokens.

A vocabulary entry with a control meaning rather than text, such as end-of-text or a chat-role marker. User text must never become one.

Learn it in the lesson: [Failure mode: injected control tokens](https://llmdojo.dev/learn/model-foundations/tokenization/special-token-injection) (Model Foundations · Tokenization: From Text to Token IDs).

## Interview questions about Special token

- [A ticket summariser crashes because tiktoken raises ValueError on a ticket that contains the literal end-of-text marker. A teammate's fix is to pass allowed_special='all'. What's your review comment?](https://llmdojo.dev/interview/q/a-ticket-summariser-crashes-because-tiktoken-raises-valueerror-on-a-ticket-that)
- [You're handed fine-tuning code whose loss behaves oddly. What do you check?](https://llmdojo.dev/interview/q/you-re-handed-fine-tuning-code-whose-loss-behaves-oddly-what-do)

## Related
- [Token](https://llmdojo.dev/glossary/token)
- [Tokenizer](https://llmdojo.dev/glossary/tokenizer)
- [Token ID](https://llmdojo.dev/glossary/token-id)
- [Vocabulary](https://llmdojo.dev/glossary/vocabulary)
- [Byte pair encoding (BPE)](https://llmdojo.dev/glossary/bpe)
- [Subword](https://llmdojo.dev/glossary/subword)
- [Glossary of every term](https://llmdojo.dev/glossary)