Lesson 6 of 9 · AI Basics
Tokens, context, and system prompts
Three insider concepts, explained in plain English: the word-pieces AI reads, the memory it runs out of, and the hidden instructions it follows.
Tokens: how AI actually reads
AI doesn't read letters or whole words. It reads tokens: small chunks of text, usually a short word or a piece of a longer one. "Cat" is one token. "Fantastic" might be two or three.
Type anything: watch it become tokens
≈ 14 tokens(9 words)
Approximate, for illustration. Real tokenizers split slightly differently, but the idea and the rough count are right.
Why care? Because tokens are the currency of AI. Usage limits, prices, and memory are all measured in them. When an AI plan says "higher limits," it means more tokens per day.
Context: the memory that runs out
Everything in your conversation, your messages, its replies, any files you attach, has to fit in the model's context window: its short-term memory, measured in tokens. Today's top models hold about a million tokens, roughly 700,000 words. Sounds infinite, but apps often use less in practice, and long chats can quietly push your earliest messages out of view.
The practical tip: start a fresh chat for each new task. If the AI seems to forget what you told it an hour ago, it isn't broken. The conversation outgrew its memory. A new chat with a short summary of what matters beats a marathon thread every time.
System prompts: the hidden instructions
Before your first message ever arrives, the chatbot has already been handed a set of instructions you never see: the system prompt. It sets the personality, the rules, and the tone. Watch what happens to one question when only those hidden instructions change:
Same question, different hidden instructions
System prompt (hidden from the user)
You are a helpful, balanced assistant.
You ask
Should I put my prices on my website?
AI answers
It depends on your business. Showing prices builds trust and filters out mismatched customers, but for custom work a 'starting at' range often works better. Consider your competitors and how custom your pricing really is.
Illustrative answers. The question never changed. Only the system prompt did.
The best part: you can write your own
Every major app gives you a place to add standing instructions of your own. ChatGPT calls it custom instructions, Claude does it through Projects, and Gemini uses Gems. Write yours once, something like: "I own a small landscaping business in St. George, Utah. Keep answers short and practical. Never use hashtags or emojis." From then on, every chat starts already knowing how you like to work. Five minutes of setup, and it pays off in every conversation after.
Last updated August 11, 2026