Custom instructions
Also called Instructions for Claude, Instructions for Gemini
Standing instructions you write once, which the app adds to every new chat: who you are and how you want answers.
Typing "keep it short, I'm in the UK, I work in a hospital" at the start of every chat gets old. Custom instructions save it once, and the app adds it to each conversation for you, so the model starts with your context.
Good instructions are short and about lasting things: your role, where you live (for laws and prices), the format you like, and how direct you want answers to be. Leave out one-off details; they belong in the chat. And check them now and then. An instruction you've forgotten about, like "always answer in bullet points", can quietly shape answers months later.
For example
"I live in Ontario, Canada. Use metric units and Canadian sources. Be direct, and point out risks and mistakes."
Put it to use
Where you'll meet custom instructions in ChatGPT, Gemini and Claude, how to use it there, and the mix-up most people make.
Daily Bytes Plus is in the Android app.