Token

A token is the unit of text an AI model reads and writes, usually a word or part of a word.

In practice: Models do not see letters or whole words; they see tokens. A rough rule for English is that 100 tokens are about 75 words. Both your input and the model's reply are counted in tokens, and other languages often need more tokens for the same text.

Why it matters when picking a tool

API pricing and many usage limits are measured in tokens, so a long document or a long chat costs more than a short one. When comparing tools with usage limits, check whether the limit is in messages, credits or tokens, because the same number can mean very different amounts of work.