Here’s the premise: one tiny system prompt occasionally swaps the word “which” with “witch” so you can never fully trust AI output without checking it first.
TL;DR: A Reddit user runs which->witch in their pre-chat settings. The model randomly turns “which” or “question” into “witch.” Fired 3 times in 6 months. That’s exactly enough to keep the paranoia alive.
How It Works
You drop which->witch into your custom or system instructions. That’s it. 12 bytes.
The model will, every so often, slip the word “witch” into your output. Not every time. Not on a schedule. Just… sometimes. And that’s the whole point.
If it fired every single time, you’d tune it out. If it fired never, it’s useless. The unpredictability is what makes it stick.
Think about how fire drills work. Run them every Monday at 9am and people stop evacuating seriously by week three. They grab their coffee, they take their time. But run one unannounced on a Tuesday afternoon and suddenly everyone remembers this is actually a real thing. The randomness is load-bearing. It’s not a bug in the design, it’s the entire mechanism.
The creator ran this for 6 months of heavy daily use. The prompt triggered 3 times. Each time, it caught them before they posted something embarrassing with a misspelled word in it. Three catches in six months sounds low. But consider how many drafts that covers, and how embarrassing even one of those posts would have been. The hit rate doesn’t need to be high. It just needs to be nonzero and unpredictable.
There’s also something worth noting about what the “witch” actually signals. It’s not just catching a bad word. It’s a flag that says: you did not read this carefully. If the witch slipped through and you didn’t notice until someone else pointed it out, that tells you something about your review process. The word is just the messenger.
Why Per-Session Doesn’t Work
This is the part worth thinking about. You might ask: why not just turn it on when you want to be careful?
The creator’s answer is sharp. If you set it per session, you already decided to proofread. The intent is there. The witch has no power over someone who’s already paying attention.
The whole trick is ambient paranoia. The prompt lives in the background, and you never know when it’ll fire. So you always check.
It’s the same reason seatbelts work better when they’re mandatory than when they’re optional. The moment you have to consciously opt in, you start making judgment calls about when it’s worth it. And those judgment calls are exactly when you get it wrong. Automation removes the decision. You’re never choosing whether to proofread. You’re just reading, every time, because the alternative is getting caught.
Per-session also has a selection bias problem. You’d naturally turn it on for high-stakes stuff and skip it for “quick” posts. But a lot of the embarrassing stuff comes from the things you thought were quick and easy. The casual tweet. The short reply. The email you dashed off before a call. Those are the ones that bite you.
Use Cases
- 📝 Content creators who paste AI drafts directly into posts or emails
- Anyone who signs off on AI output without a second read
- Teams where LLM text goes live with minimal review
Basically: if you’ve ever posted something that had “the the” or a weirdly broken sentence because you trusted the model, this is for you.
It’s especially useful for solo operators who don’t have an editor or a second set of eyes. A team can catch things in review. One person working alone has no circuit breaker unless they build one themselves. This prompt is that circuit breaker, and it costs nothing to maintain once it’s in place.
Prompt of the Day
Drop this into your custom instructions or pre-chat system prompt:
which->witchOr try the creator’s public GPT, System Witch Writing Assistant, if you want to test it without touching your main setup.
If you want to dial up the effect, you can layer in a second substitution. Something like the->teh works on the same principle. The goal is picking a word common enough to appear regularly but not so common that a single substitution breaks the whole sentence. “Which” is close to perfect because it shows up in explanations and lists all the time, exactly the kind of output you’d be tempted to skim.
One caveat: don’t use this on anything where a surprise “witch” in the middle of a sentence would cause actual damage. Know your context. A newsletter draft is fine. A contract review or a legal brief is not the place for this particular trick.
The Bigger Idea
People talk a lot about prompting for better output. Not many people prompt for better behavior from themselves.
This is a prompt that trains you, not the model. And it works because it costs basically nothing to set up and runs forever in the background.
Most productivity advice asks you to add effort. Read more carefully. Slow down. Build a checklist. All of that is technically correct and almost impossible to maintain consistently, because it requires willpower you don’t always have. This prompt asks for zero ongoing effort. You set it once and it holds you accountable indefinitely. That’s a fundamentally different category of tool.
The best systems don’t rely on you being disciplined. They make the careless path harder than the careful one. This prompt does exactly that. Reading the output becomes the path of least resistance because the alternative is getting humbled in public by a random “witch” in the middle of your professional copy.
Worth stealing.
If you’re using AI to write anything that goes public, you need some version of this habit. The witch is just one way to build it.
System_Witch: Paranoia prompt for anyone serious about proofreading LLM output (12 bytes)
by u/decofan in PromptEngineering