Custom instructions are the highest-return ten minutes you can spend in ChatGPT. They apply to every chat, so a small improvement compounds across everything you type.
The problem is the blank box. Most people write their job title and "be concise", then see no difference. This template gives you six blanks instead. Fill them in honestly and the answers change.
The template
Box 1: What should ChatGPT know about you?
I work as [1: role] at [2: type of organisation]. What I produce
is mostly read by [3: audience and what they care about].
I already know [4: what you do not need explained]. Skip that.Box 2: How should ChatGPT respond?
Default format: [5: how you like answers laid out].
Never: [6: the three habits that annoy you most].
If you are unsure, say how unsure and what would settle it.
If I am wrong, say so in the first line.Blank 6 does the heavy lifting. Positive instructions like "be concise" compete with the model's defaults. A specific never list replaces them.
Three filled-in examples
Operations manager
I work as an operations manager at a 200-person logistics company.
What I produce is mostly read by the leadership team, who want the
decision and the cost, not the method.
I already know Excel, basic finance and our industry. Skip that.
Default format: answer first, then at most five bullet points.
Never: preamble, restating my question, or a summary paragraph at
the end.Freelance copywriter
I work as a freelance copywriter for B2B software companies. What I
produce is read by busy buyers who skim.
I already know copywriting fundamentals. Skip them.
Default format: give me three options, not one, for anything
headline-length.
Never: the words unlock, elevate, seamless or game-changer; em
dashes; exclamation marks.Teacher
I teach secondary school history. What I produce is read by
students aged 14 to 16 and sometimes their parents.
I already know the curriculum. Skip background on the topic unless
I ask.
Default format: plain language a 14-year-old would follow.
Never: American spellings, invented quotes, or dates you are not
sure of.A custom instructions prompt to fill it for you
If you would rather not write it cold, paste this into a new chat and answer its questions:
Interview me to write my ChatGPT custom instructions. Ask one
question at a time, no more than eight in total, about my work, my
audience, what I already know, and what annoys me in AI answers.
Then write both boxes in plain sentences, under 1,200 characters
each.Character limits
Each custom instructions box has a character counter under it, and the limit has sat around 1,500 characters per box. Project instructions allow more room, but longer is not better: past a few hundred words, the later lines start to get less attention than the early ones. Put the rules you care about most at the top.
Questions people ask
What is the ChatGPT project instructions character limit?
Project instructions allow considerably more text than custom instructions, and the exact limit has changed over time, so check the counter in the project settings. Aim for under 400 words regardless.
Do custom instructions apply to projects?
Yes. They stack with project instructions, and where they conflict the more specific project instruction usually wins.
How often should I update them?
When something annoys you twice. Add it to the never list the same day.
Where to take this next
For where custom instructions end and projects, files and memory begin, read ChatGPT Projects done properly. If you would rather have instructions written from your actual role, The Pack generates them from your LinkedIn profile, with install paths for ChatGPT, Claude, Gemini and Copilot.
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