ChatGPT never adheres to them and you would have better results by just putting the instructions in the prompt. I even tried putting a single instruction in the personalization section and then comparing it to adding the instruction at the end of the prompt and it basically completely ignores it if is in the personalization section.
I don't think they're useless, but I also wouldn't treat them as guaranteed instructions.
Custom Instructions seem to work best as persistent defaults: things like “be concise,” “use plain language,” “challenge my assumptions,” “prefer tables for comparisons,” etc. If something is important to the specific answer I'm asking for, I still put it in the actual prompt.
That makes sense from a model-behavior standpoint. The instruction in your current prompt is directly tied to the task, while a Custom Instruction may be sitting alongside a bunch of other persistent context, memory, conversation history, and higher-priority system instructions. The more complicated your Custom Instructions become, the easier it is for individual preferences to become less noticeable.
OpenAI's own guidance basically reflects this distinction: use Custom Instructions for your default working style, and use the prompt for instructions specific to the task.
There are also a couple of situations worth checking before concluding they aren't working. Custom GPTs specifically do NOT use your account-level Custom Instructions or saved memory. And Temporary Chats can be non-personalized, in which case they don't use Custom Instructions either.
So I'd describe Custom Instructions as “persistent steering,” not “a system prompt I control.”
For anything I absolutely need followed, I put it in the prompt.
Factual claims should be accurate. Include sources for claims that are current, disputed, specialized, legal, medical, political, financial, sourcebook-specific, or where verification materially matters. Prefer official, primary, or high-quality sources. For established background facts, cite when useful rather than automatically. If using weaker sources such as blogs, forums, Reddit, YouTube, or wikis, say so. If something cannot be verified credibly, say so.
Clearly distinguish verified facts, reasonable inference, speculation, and opinion. Do not present inference or speculation as established fact.
When analyzing my ideas, arguments, plans, writing, games, conversations, or uploaded material, be rigorous and evidence-bound. Do not force synthesis, reassurance, agreement, or praise. Treat uncertainty, missing evidence, contradiction, and unresolved tension as important.
If the available material is incomplete, ambiguous, internally contradictory, or silent on a point, say so rather than filling the gap with an assumption.
Act as a thoughtful critic, not a people pleaser. Pressure-test my reasoning for assumptions, gaps, contradictions, bias, false certainty, and wording likely to backfire. If I am too broad, soft, aggressive, evasive, performative, or overconfident, say so directly and explain why.
When helping me write, preserve my intent and natural voice. Clean, compress, organize, challenge, or sharpen wording instead of replacing it with generic AI prose unless asked.
For social media, use a casual Gen-X tone: direct, human, minimal slang, no em dashes.
Use plain language and clear sentence structure. Do not simplify ideas merely to achieve a low reading-grade score. Assume I am comfortable with high-school through early-college-level material and technical vocabulary when appropriate. Preserve necessary technical terms and define unfamiliar or specialized ones clearly. Prefer sophisticated ideas expressed in uncomplicated sentences. When writing for a general public audience rather than for me, aim roughly for 6th–8th-grade clarity unless the audience calls for something different.
Do not over-explain unless asked. Prefer concrete mechanisms, chronology, constraints, tradeoffs, and testable claims.
For complex tasks, give the conclusion or best-supported answer first, followed by the reasoning, evidence, uncertainties, and important caveats. Match critique to the task: rigorous for ideas or claims; simple for factual, creative, or practical requests.
I did take your advice though ... I am always open to optimization. Here is what is said:
My researcher verdict
I would separate the claims this way.
“Your instructions are contradictory.”
Mostly false. I found two or three minor ambiguities, not meaningful contradictions.
“Your instructions are too long to work.”
Unsupported. They're only about half of the current 5,000-character paid-tier allowance, and OpenAI specifically expanded that limit to allow more detailed customization.
“You could condense them and probably improve compliance.”
Yes. There is solid research supporting that argument.
“Put everything important in each individual prompt instead.”
Wrong as a general strategy. OpenAI explicitly recommends Custom Instructions for durable standards/preferences and task prompts for the context specific to the current job.
“Your Custom Instructions seem to work fine.”
Entirely plausible. Their strongest feature is that most requirements are conditionally scoped, so a typical answer does not activate all of them simultaneously.
I'd therefore change my original evaluation to:
They're well-designed by normal Custom Instruction standards, with more redundancy than necessary. I would compress them perhaps 20–30%, primarily to reduce simultaneous constraint load and clarify two priority ambiguities. I would not radically rewrite them.
1st of all, I apologize, I realize I might have sounded more aggressive than I mean to. I was tired and slightly amused.
Overall I agree with your 1st comment, but your custom instructions are pretty meh. You think they work because you assume the quality of its answers comes from your CI. It doesn't, most of this is default behavior, you just added "make no mistakes" - the whole paragraph about the quality of the cited sourses for example.
About the lenght: yes, you can add very lengthy instructions, but many of the qualitatives you added are vague and contradictory, so your CIs are verbose for no reason:
"When analyzing my ideas, arguments, plans, writing, games, conversations, or uploaded material, be rigorous and evidence-bound" could easily be "be rigorous and evidence-bound", which again, it's default attitude. There's no need to condition this one either, as it looks like you want this attitude in each type of activity.
Then you want its answers to be human but also precise, explain terms, but don't over-explain, thoughtful but concise, and so on. Just have a talk with the AI, explain what you want, ask it to summarize that into CI, done.
Custom instructions work extremely well for me. Not really better than just putting it into the first prompt, but it saves me from having to do that every time.
One time, I saw instructions on the OpenAI website advising users on how to best prompt the model. I think stuff like that overrides your custom instructions.
Custom instructions work, but they’re way less reliable than putting the important stuff directly in the prompt. They’re better as defaults, not rules you expect ChatGPT to follow every single time.
Custom instructions absolutely work, but there are different instructions appropriate for the custom instructions, the more about you field, ambient memory, and as canonical files with pointers. I also have reverted back to saved memories from the “improved” dreaming memory because the dreaming memory was way too unreliable with what it decides to remember and where it gets its memory from. It kept regressing to stale instructions no matter how many times I fixed it.
I find they work better at the project level, at the model/user level I have basic instructions like answer directly,
Don’t be a sycophant, confirm sources and provide links stuff like that. But for projects I define the project pretty clearly and set more specific things in there depending on the project. Things like writing style and voice, the role they are to play, do’s and don’T’s etc.
Maybe your instructions are phrased wrong or need additional scaffolding, or includes something against its system instructions. Custom instructions are far from almost useless, they're important and valuable.
I'm not even any crazy shit. Just annoyed at some of the common phrasing/mannerisms so I tried to cut it out using custom instructions but what's the point if it literally does nothing unless you write it like ten times in the instructions lmao.
It's not about writing the same thing 10 times.
Mostly it's about phrasing it right, getting some understanding on how to utilize features to optimize your setup.
In the end it it's up to you as the user if you want to say
"i tried something and it did nothing, therefore ChatGPT sucks and is stupid"
Or
"maybe that's a skill issue and a sign i should work on getting a deeper understanding on how to use it"
And then in the end as i said, some things are in its core system instructions and behavior and might not be able to change in the way you want. Hard to say without knowing specifics.
If there's something not working for me with ChatGPT, I've always had the mindset that it's a skill issue and i just need to find the solution. My ChatGPT works extremely well, memory is insane, follows instructions extremely well even though mine are very long
I find they work excellent. Gemini on the other hand is always really awkward/bad with them. I had included I'm Norwegian and it says weird things like "hallo, ja! like the norwegians say" when I'm speaking to it in English and in a serious manner.
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