ChatGPT Custom Instructions: 5 Steps to Set Yours
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Last checked: 10 November 2026
Many people type the same thing at the start of every chat: who they are, how they like answers written, what to avoid. ChatGPT custom instructions let you write that once. This guide shows what they are, what to put in them and five checks so they help instead of causing odd answers.
It is based on OpenAI’s help page ChatGPT Custom Instructions. It has not been tested by us, and the options may change.
What custom instructions do
OpenAI describes custom instructions as a way to give ChatGPT standing preferences that apply to your future chats. They are available on all plans on web, desktop, iOS and Android. On web and desktop you find them in Settings, then Personalization. On mobile the entry is called Customize ChatGPT. There is an Enable customization switch so you can turn them on or off.
OpenAI states they apply to future chats only, so older conversations do not change.
How they differ from memory
Memory is what ChatGPT may pick up over time. Custom instructions are what you write yourself on purpose. That makes them easier to control: you can read them, change them and delete them. If you only fix one setting, fix this one.
5 steps to write good custom instructions
- Say who you are in one line. For example, “I run a small bakery and write for customers, not experts.” Keep it to what helps an answer, not private details.
- Say how you want answers. Short or long, plain words, bullet points, a friendly tone. One or two sentences is enough.
- Say what to avoid. For example, “Do not use jargon” or “If you are not sure, say so instead of guessing.”
- Stay within the limit. OpenAI says the limit is 1,500 characters on Free and Go, and 5,000 on Plus, Pro, Business, Enterprise and Education. Shorter is usually clearer.
- Test, then adjust. Ask one normal question, read the answer and change one line if needed. Change one thing at a time so you know what helped.
A worked example (illustration only)
Here is a short set of instructions a shop owner might write. It is an example, not something we tested.
- About me: I run a small shop and write messages to customers on WhatsApp.
- How to answer: Use simple words, keep replies under 100 words, and be polite.
- Please avoid: Do not invent prices or opening hours. If you need a fact, ask me.
The last line matters most. It tells the assistant to ask rather than guess, which lowers the chance of a confident wrong answer.
What to do this week
- Open Personalization and read what is there now.
- Write three short lines: who you are, how you want answers, what to avoid.
- Remove anything private about customers or family.
- Ask one normal question and see whether the answer improved.
What can go wrong
- Too much detail. Long instructions can pull every answer in the wrong direction.
- Private information. OpenAI says custom instructions are included in a data export, so do not store secrets in them.
- Old instructions. A job or business change can make them wrong. Review them now and then.
- Believing it always follows them. It may not, so still read each answer.
Common mistakes
- Writing a long personal biography instead of three useful lines.
- Putting a customer’s name or number in the instructions.
- Expecting old chats to change after you edit them.
- Forgetting they are switched on and wondering why every answer sounds the same.
OpenAI also notes that people who open a shared link to your chat do not see your custom instructions, and that they are deleted within 30 days of account deletion.
Three versions to try, from short to detailed
If you are not sure how much to write, start small and add only when an answer disappoints you.
- Version one, one line: “Use simple words and short answers.”
- Version two, three lines: who you are, how you want answers, and one thing to avoid.
- Version three, for a specific job: add the kind of customer you write to and the tone you want, such as polite but direct.
Most people find version two enough. Keep a copy of your instructions in a note on your phone so you can restore them if you ever change them by mistake. When an answer comes back wrong, ask yourself whether the instruction was unclear before blaming the tool, and rewrite that single line first. Review the whole set every few months, because the way you work changes and old instructions can quietly push answers in a direction you no longer want.
Where to go next
Read how to check an AI answer before you use it, and our ChatGPT privacy settings guide. For plain definitions see AI in Plain Words, or use Start Here to pick a first step.
Frequently asked questions
Do custom instructions work on the free plan?
OpenAI says they are available on all plans, with a shorter character limit on Free and Go.
Will they change my old chats?
No. OpenAI says they apply to future chats only.
Where do I find them on my phone?
On mobile the entry is called Customize ChatGPT. Names can change, so check the current help page.
Can I switch them off without deleting them?
OpenAI describes an Enable customization toggle for that.
Sources: OpenAI Help Center, “ChatGPT Custom Instructions” (https://help.openai.com/en/articles/8096356-chatgpt-custom-instructions), last checked 10 November 2026. It supports the plans and platforms, the locations in the app, the character limits, the toggle, future chats only, the data export, deletion after account deletion and shared links. The worked example and checklist are our own general good practice, not from OpenAI.
