System prompts — telling AI who to be
Every AI conversation has a hidden first instruction. Knowing how to set yours is the difference between a generic answer and one calibrated to you.
::TL;DR · the whole lesson in three lines
- MOVEEvery AI conversation has a hidden first instruction. Knowing how to set yours is the difference between a generic answer and one calibrated to you.
- DRILLYou're going to write your own personal system prompt — short, specific, yours — then install it in one tool and use it for one real task today. Total time, about fifteen minutes.
- WINYou can name the system prompt slot in the tool you actually use, and you've installed text in it.
::concept · what's actually happening
Before you type your first message, the AI has already been told who it is. That hidden first instruction is the system prompt — a separate slot from your chat messages where the model is given its role, its rules, and the context it should carry into every reply. The chat you see is the second layer. The system prompt is the foundation under it. Most people never touch this slot, which is why most AI answers feel generic — the model is defaulting to 'helpful general assistant' instead of 'helpful assistant for you, specifically.'
read full concept · 4 more paragraphs →collapse concept ↑
Every major tool exposes this differently. In the Claude API and Claude Code, it is a literal field called `system`. In ChatGPT, it lives under Settings → Personalization → Custom Instructions (two boxes: what to know about you, how to respond). In Gemini, it is under Settings → Personalization. Same idea in all three: text the model reads once at the start of every conversation, before it ever sees what you typed. You write it in plain English. No code. No special syntax. Just sentences.
A good system prompt does three things. It tells the AI who you are (one or two facts that matter — your job, your city, your context), it tells the AI how to respond (length, tone, format you actually prefer), and it tells the AI what to skip (preamble, disclaimers, hedging you don't need). That's it. The mistake most people make on their first try is treating the system prompt like a wish list — twenty lines of personality, six contradictory rules, and a paragraph of philosophy. The model gets confused and falls back to generic behavior anyway.
Short and specific beats long and aspirational. Five to fifteen lines is the sweet spot for a personal system prompt. Each line should be a rule the model can actually act on in the next reply. 'Be more creative' is not actionable. 'When I ask for ideas, give me five short options labeled A through E, then stop' is actionable. The test is simple: if you can't picture the exact shape of the next answer the rule would produce, the rule is too vague.
One last thing worth knowing: the system prompt is yours. It travels with you across conversations in that tool. Set it once thoughtfully and every chat for the next month inherits it. That's the actual lever. The chat box is the keyboard. The system prompt is the instrument it's playing.
::drill · do the thing
You're going to write your own personal system prompt — short, specific, yours — then install it in one tool and use it for one real task today. Total time, about fifteen minutes.
::L19 drill · copy-paste into any AI chat
Open a blank note (Notes app, paper, anywhere). Title it "My system prompt v1." Then fill in this template — answer each line in one sentence, max: WHO I AM: I am [your role / what you do]. I live in [city or context]. The work I bring to AI is mostly [the 1-2 categories you actually ask about]. HOW TO RESPOND: Default length: [one sentence / one short paragraph / structured bullets — pick one]. Default tone: [direct and plain / warm but brief / formal — pick one]. When I ask for options, give me [number] and stop. When I ask for a decision, recommend one and name the trade-off. WHAT TO SKIP: Skip preamble like "Great question." Skip closing offers like "Let me know if you want more." Skip disclaimers unless the topic is legal, medical, or financial. WHAT TO ASK FIRST: If a request is ambiguous, ask one clarifying question before answering. Otherwise proceed. Once you have all four sections filled in, you have a v1 system prompt. Install it in your tool of choice (see drill steps), then run one real task through it.
::steps
- 01Open your note and fill in the four-section template above. Keep every line to one sentence. If you cannot picture the exact reply shape a rule would produce, rewrite it more concretely.
- 02Read the whole thing out loud once. If any two lines contradict each other (e.g. 'be brief' and 'always show your reasoning'), delete one. Contradictions are the number-one reason system prompts fail.
- 03Pick your tool. ChatGPT: Settings → Personalization → Custom Instructions. Gemini: Settings → Personalization. Claude (free chat): Settings → Profile (limited) — for full control use Projects, where each Project has its own system prompt slot.
- 04Paste your prompt into the appropriate boxes. In ChatGPT, the 'about you' lines go in the first box, the 'how to respond' lines go in the second. In Gemini and Claude Projects, it's one combined field.
- 05Open a new chat — important, the system prompt only applies to chats started AFTER you save it. Run one real task you actually need done today: a draft email, a meal plan, a code review, a decision matrix.
- 06Compare the reply to what you'd usually get. Note one thing that improved and one thing that's still off. Open your note and tweak exactly one line based on what you saw. That's v2.
- 07Save the note somewhere you'll find it. You'll iterate on this prompt for months — it's a living document, not a one-shot.
::outcome · what should be true
- You can name the system prompt slot in the tool you actually use, and you've installed text in it.
- Your next chat starts with a different shape — shorter, more direct, or formatted the way you asked — without you having to remind the model in-message.
- You have a saved note titled 'My system prompt v1' that you can edit and reuse across tools.
- You can articulate at least one rule you wrote that changed the reply, and one rule that didn't work and needs revision.
- You stop typing 'be concise' at the start of every chat, because the system prompt already says it.
::trap · the most common failure
The most common failure is writing a system prompt that is too long and internally contradictory. People stuff in twenty rules, three personality descriptions, and contradictory length instructions ('be thorough' next to 'be brief'). The model resolves the conflict by ignoring most of it and reverting to generic behavior. If your prompt is over fifteen lines or contains two rules that pull opposite directions, cut until it fits on one screen and every line points the same way. Short and consistent beats long and aspirational every time.
::other lessons at Novice level
I'm scared of AI · the calm starting point
Before any lesson, the feeling. Whether you are scared, skeptical, exhausted by the hype, or quietly excited and hiding it — this is the door. None of the feelings are wrong. The path is yours.
What AI actually does — autocomplete at huge scale
Strip the magic feeling off. Get the working model of what AI is doing under the hood, so the rest of the curriculum has a foundation.
Your first real prompt — be specific, not polite
Stop typing into AI like you're texting a friend. The prompt is the entire skill at this level.
When AI gets it wrong — see a hallucination, on purpose
You will not respect the verify rule until you watch AI lie to your face with full confidence. Do it now, on a low-stakes question, where the cost is zero.
::part of the AtomEons /learn curriculum · 45 lessons · 5 levels · cc-by 4.0