Techniques5 min read
How to Write a System Prompt (With a Full Working Example)
A system prompt sets an AI assistant's role, rules and format for a whole conversation. Learn what belongs in it, how to order it, and see a full example.
Role & context
System prompts, roles and context: framing the model
Role and context prompting means telling the model who it is serving, in what situation and under which rules before you give it the task. A system prompt sets that frame for a whole conversation. A role such as “you are a senior tax accountant” helps only when it brings real constraints with it, like audience, standards and what to do when unsure.
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Structured outputIntermediate
Your app parses the model’s JSON, but sometimes the reply starts with “Sure! Here is the JSON:”. What is the most robust fix?
AAdd “please” to the prompt
BUse structured-output mode with a schema, then validate
CLower the temperature to 0
DStrip the first line of every reply
Sample question · Role & context
You are building a support bot. Where should the rule “Never promise refunds; hand off to a human instead” go?
- AIn the system prompt, as a standing rule
- BRepeated in every user message
- CIn the first assistant reply
- DNowhere, the model will infer it
Show the answer and why
A. In the system prompt, as a standing rule Standing rules that apply to the whole conversation belong in the system prompt. User messages change every turn and are also where untrusted input arrives.
What the questions test
- What belongs in a system prompt vs. a user message
- When a persona helps and when it is just decoration
- Giving background the model cannot know
- Keeping long conversations on track
What you’ll learn
- How to structure a system prompt for a real product
- How to write roles that change behavior, not just tone
- How to pass background documents and user details cleanly
- How to handle conflicting instructions
How to practice it in TokIQ
- 1. Open Role & context. Pick it from the topic list on the Quiz tab. It is included in the free plan.
- 2. Answer one question at a time. You see right away whether you were correct.
- 3. Tap Why? Read the short explanation and answer three follow-up questions on the same idea.
- 4. Watch your accuracy. The Progress tab shows how Role & context compares with your other topics.
Role & context: common questions
What is a system prompt?
A system prompt is the instruction block that sets the model’s role, rules and context for a whole conversation, before any user message. Products use it for tone, scope, safety rules and output format.
Does “act as an expert” improve answers?
Only a little on its own. A role works when you add what that expert would know and care about: the audience, the standards, the format and what to do when information is missing.
Further reading
Basics6 min read
Prompting ChatGPT vs Claude vs Gemini: What Carries Over
Do prompts work the same in ChatGPT, Claude and Gemini? Most principles transfer. Here is what differs, and how to test a prompt across models without guessing.
Basics6 min read
What Is Prompt Engineering? A Practical Guide With Examples
Prompt engineering is the skill of writing inputs that get reliable results from AI models. Learn the parts of a good prompt, with before-and-after examples.
More topics
Practice role & context a few questions a day.
Short quizzes on real prompting decisions, with an explanation for every answer. Free to start on iPhone and Android.
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