Most people treat every new AI chat like a first date. They explain their style, their format, their pet peeves, and then do it all again tomorrow. This approach does something different: you write the instructions once, and they travel with you.
Captain YAR here. A post on r/PromptEngineering by u/AgentPouchHQ caught my eye. It has 30 upvotes and it describes a trick that costs nothing. It’s a short rules file, about 15 lines, that you paste at the start of every new chat or project.
The Key Idea
The model doesn’t remember you between chats. You explain how you like things done, it nails it, and three chats later it does everything the old way again.
The fix is to stop relying on the model’s memory. Put the memory in a document you control. The doc does the remembering, so the model doesn’t have to.
Old Way vs. New Way
The old way: You type your preferences from scratch in every chat. Some days you remember half of them. The AI repeats the same mistake, you correct it again, and you lose ten minutes you’ll never get back.
The new way: You keep one short rules file. You paste it in at the start. Every chat begins with your standards already loaded. When the AI slips, you fix the file once, not the conversation again and again.
The file is the part that compounds. The chat is disposable.
What Goes in the File
The original post splits it into four parts. Here they are, with a few notes from me:
- How you want answers. Example: short first, details only if I ask. This alone saves a lot of scrolling.
- Things to never do. Example: no inventing facts, say “not sure” instead. This is your guardrail against confident nonsense.
- Your context. What you’re building, who it’s for, and which tools you use. The AI stops guessing about your situation.
- A pre-answer checklist. Did it follow your format? Did it ask when something was unclear? You’re telling it to check its own work before replying.
Practical Steps
- Open a blank note. Any text file works. Keep it somewhere you can copy from in two seconds.
- Write the four sections above. Aim for roughly 15 lines. Short beats thorough here, because a file you won’t paste is useless.
- Paste it at the start of every new chat or project. If your tool has a dedicated spot for instructions, use it. Custom GPTs, Claude Projects, and Cursor all have one, so you may only need to set it up once.
- Add one line every time the AI makes the same mistake twice. That’s the habit that makes the file good. After a month it’s weirdly tailored to how you work.
- Trim it now and then. If a line no longer earns its place, cut it.
Lines the Community Swears By
The comments are where this gets useful. People shared the one line that made the biggest difference for them:
- “If you’re unsure, ask me before guessing.” One commenter made this the very first rule and said it cut their hallucination headaches by around 80%. 🧭
- “Never invent facts, state what you do not know instead.” Another reader called this their biggest win. A short rules file loads the same priorities every time: format, sources, and what counts as an acceptable answer.
- “When a request is ambiguous, list your assumptions before answering.” This makes the gaps visible so you can correct them early, instead of finding out three paragraphs later. ⚓
Notice the pattern. The best lines don’t tell the AI to be smarter. They tell it what to do when it isn’t sure.
One Fair Pushback
One commenter asked whether we’ve moved beyond such a basic document, and noted the post doesn’t say what type of file it is, where it lives, or how it’s referenced. That’s a fair point. Here’s how I’d answer it:
- Type: plain text or Markdown. Nothing fancy.
- Where it lives: in your project’s top folder if you use a coding tool like Cursor, or in the instructions field if you use Projects or Custom GPTs. Otherwise keep it in a note you can paste from.
- How it’s referenced: pasted at the start, or loaded automatically by the tool.
More advanced setups do exist, but this one has a very low barrier to entry, and you can build on it later. Start simple, then grow it.
Your Turn
Open a blank note right now and write the first five lines. Start with the rule that would have saved you the most pain this week. Then paste it into your next chat and see what changes. 🏴☠️
And tell me: what’s the one line in your instructions that made the biggest difference? Drop it in the comments, and I’ll steal the best ones for the next post!
Frequently Asked Questions
Q: Do I need a separate file, or can I put this in my tool’s custom instructions?
Custom instructions work just as well. Gemini Gems, Copilot settings, Custom GPTs, and Claude Projects all have a field where the same text goes, so the file is really just a portable copy. Keep a file if you switch between tools or work in coding setups, since you can paste the same text anywhere without rewriting it.
Q: Which rule should go first?
Commenters picked different ones, and each has a reason. One put ‘if you’re unsure, ask me before guessing’ at the top and reported a big drop in made-up answers. Another leads with ‘never invent facts, say what you don’t know,’ and a third asks the model to list its assumptions whenever a request is ambiguous. Try one for a week and see which one changes your results most.
Q: How long should the file be?
Keep it under a page, and the 15-line version from the post is a good target. One commenter noticed that once the doc turns into a manual, the model starts weighting the wrong rules and the same mistakes return in new forms. Long lists dilute the lines that matter. Cut anything you have not needed in weeks.
Q: Won’t the list keep growing forever?
It will if you only ever add. The habit that helps is one rule in, one rule out. When a new line makes an older, narrower rule redundant, delete the old one so the file stays short and sharp.
Free trick: put a rules file at the top of your project so your AI stops repeating the same mistakes
by u/AgentPouchHQ in PromptEngineering