Settings that persist across chats
Custom instructions save the standing context and answer rules you would otherwise repeat in every conversation — explain for beginners, lead with the conclusion, answer in English, do not overuse tables — and apply them across chats.
In ChatGPT these live under personalization settings. Other assistants offer something similar under names like profile, response settings, or user instructions. Length limits and where they apply differ by service and plan.
What to put in them
- Your work, and what you mainly use AI for
- Your intended reader, and the level of explanation you want
- Preferred tone, length, use of headings and bullets
- Terminology to follow, things to avoid, how you want work checked
- What to do when information is missing
Keeping only the conditions that always apply works better than writing a long self-introduction. Project names, deadlines, and one-off source material belong in the prompt for that conversation.
How this differs from prompts, memory, and GPTs
A prompt is the request in front of you. Custom instructions are the answering policy you reuse across conversations. Memory records preferences and facts from your conversations and applies them later, which is not limited to rules you wrote yourself.
GPTs are separate, purpose-built versions of ChatGPT that combine their own instructions, knowledge files, and tools. Use custom instructions to shape ordinary ChatGPT to your preferences; use a GPT when you want a shareable assistant dedicated to one job.
Getting them right
After setting them, try a few ordinary short questions and trim rules that are too strong or contradict each other. A hard requirement such as always give three options will fire on simple questions too and make answers feel unnatural.
Custom instructions are not a place to store secrets. Do not enter passwords, API keys, customer data, or personal information you do not want retained. Instructions are also not guaranteed to be followed, so have a person check anything important before it ships.