System Instruction Builder
Most AI tools have a "system instruction" field that shapes every response in the conversation. Most people leave it blank or write "be helpful." This tool builds a real one.
Pick a template, customize the fields, and copy the result. Paste it into ChatGPT's "Custom Instructions," Claude's "System Prompt," or Gemini's "System Instructions." Same idea, different names.
Who should the AI be? This shapes everything else.
What's the situation? Project background, audience, existing constraints.
Languages, frameworks, libraries. Prevents the AI from suggesting things you can't use.
What should the AI avoid? One rule per line. These become hard constraints.
Pick a template or start filling in fields — the system instruction builds here in real time.
Why System Instructions Matter
Every conversation with an AI starts with two invisible questions: "Who am I?" and "How should I behave?" Without a system instruction, the AI defaults to "generic assistant" — helpful, but unfocused.
A good system instruction is like briefing a contractor before a job. You wouldn't say "do some work on my house." You'd say "you're a plumber, the kitchen sink is leaking, I have copper pipes, and I need it fixed today without replacing the countertop."
Same energy. Different medium.
What Each Field Does
Role
The single most impactful field. "Senior React developer" produces different code than "junior developer learning React." The AI adjusts its vocabulary, assumptions, and level of detail based on the role.
Context
Background that prevents the AI from starting from zero every time. "I'm building a fitness app" means something different than "I'm maintaining a legacy banking system."
Rules & Don'ts
The underrated field. "Don't add features I didn't ask for" alone saves hours of "I also took the liberty of refactoring your entire codebase" responses. Constraints are love letters to your future self.
Where to Paste It
ChatGPT: Settings → Personalization → Custom Instructions
Claude: Create a Project → System Prompt field
Gemini: Gems → Create → Instructions field
API: The system message in your API request
The names change. The concept doesn't. Every AI tool has a way to set persistent instructions that apply to the whole conversation.
Nothing leaves your browser. The instruction is generated locally from the form fields. I don't see your role definitions, your project context, or the creative ways you tell AIs not to add unsolicited features.