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Understanding AI

Custom instructions

Stop editing every answer. Set it once, and it applies to everything after.

your instructionsset once, in settingsyour prompttyped every timereadsbothanswerevery message, every new chat, without you asking again

The prompt that writes yours

Paste this into whichever tool you use. It interviews you about your job and what you keep having to fix, then writes the set for you and hands it over ready to paste into the settings. Nothing to fill in.

I want to write a set of custom instructions that will apply to every conversation I have with you, so your answers come back in the format and style I actually want.

Interview me first. Ask me one question at a time, and wait for my answer before the next one. Cover: what I do for work, what I mostly use you for, how I like information presented, what I find myself editing or deleting after you have written something, and anything about the way you write that irritates me.

Keep going until you have enough to be specific rather than generic.

Then write me a set of custom instructions of under 150 words. Prioritise the few rules that will change the most about your output and leave out anything that is only nice to have, because a long list gets diluted and quietly ignored.

Give me the finished set in a code block so I can copy it straight into my settings. Then tell me which of my answers drove each line, and what you deliberately left out and why.

What it actually is

Custom instructions are a box in the settings. Whatever you put in there gets read alongside your prompt, every single time you send one, in every new chat. It is not remembering anything, and it is not learning from your corrections. It is re-reading your instructions before it reads your question, every time.

The useful way to think about it: it is what you would tell someone at work about how you like to receive information. Keep it short, bullet points where you can, skip the preamble, do not use acronyms. You would not repeat that in every email. You would give it to them once, in their onboarding.

How to actually find it

It is a settings screen, and it takes about twenty seconds. The names move around as the apps get updated, so go looking for the idea rather than an exact menu item: anything that says custom instructions, personalisation, preferences, or asks how you would like the assistant to respond.

1

Open settings

Usually behind your name, your profile picture, or the three dots in a corner. On mobile it is often under a menu icon rather than on the main screen.

2

Look for personalisation

In ChatGPT it sits under Personalisation. In Claude it is with your profile settings, phrased as how you would like Claude to respond. In Copilot it is under the personalisation or preferences area. Same idea, different labels.

3

Write in the box and save

There is usually one free text box, sometimes two: one about you, one about how you want answers written. The second is the one that does the heavy lifting. Save it and it applies to every new chat from then on.

If you cannot find it at all: search the settings for the word instructions, or check whether you are on a work account. Some organisations lock these settings down.

If yours has, set it up in your personal account instead, or ask whoever runs it internally, because it is a harmless thing to allow. It changes how answers are written for you, nothing else.

What to put in, and what to leave out

Worth including

  • Length. The single highest impact line you can write.
  • Spelling and register. British English, plain words, no corporate filler.
  • Format. Bullets or prose, and how long a list is allowed to get.
  • What to leave out. Preambles, summaries, restating your question back at you.
  • What you already know, so it stops explaining the basics of your own job to you.

Leave it out

  • Twenty rules. Long lists get diluted and quietly ignored.
  • Facts about projects that change. That is what a chat or a project file is for.
  • Anything you only want occasionally. Ask for it in the moment instead.
  • Vague vibes. Be professional means nothing. Under 150 words means something.

What a good one looks like

An example, not a template to copy wholesale. Yours should name your job and the things you personally keep deleting. Notice how short it is, and that every line changes something concrete about the output.

Keep answers short. Lead with the answer, then the reasoning if it is needed.
Use British English.
No em dashes. No bullet lists longer than five items.
Skip the preamble and the summary at the end. Do not restate my question back to me.
If you are not confident, say so rather than hedging your way through it.
I work in insurance, so assume I know the industry basics and do not explain them.

What this will not do

It is a strong steer, not a hard rule. On a long conversation the model drifts back towards its defaults, and if what you asked for in the moment conflicts with your instructions, the moment usually wins. That is mostly what you want, but it means you will still catch the odd em dash.

And it changes how answers are written, not whether they are right. If you want fewer confidently wrong answers, that is a different job, and the best single line for it is giving it permission to say it does not know.

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