How to set custom instructions in ChatGPT on Mac: 2026 steps for both apps

Custom instructions tell ChatGPT who you are and how you want it to answer. You write them once, and ChatGPT applies them to new conversations. That saves you from retyping the same background in every chat. This page covers the Mac, where the app names and screens changed in 2026. It shows the path in the older app, the path in the new desktop app, and what to do when your instructions seem to be ignored.

Which ChatGPT app you have on your Mac

On July 9, 2026, OpenAI renamed the original Mac app ChatGPT Classic. A new ChatGPT desktop app combined Codex into one product. According to 9to5Mac, the way forward is the new app. The two apps can be installed side by side. Classic looks more native to the Mac, which may matter to some people. 9to5Mac gives no version numbers for either app, so the app name is your safest guide.

• Open Finder, then Applications, and look for ChatGPT Classic and ChatGPT.
• Open the app you plan to use. If its menu bar and Settings look different from the steps below, you may have the other app.
• Follow only the path that matches the app you open. Skip the steps for the other app.

Set custom instructions in ChatGPT Classic

The Classic path matches most older guides. iGeeksBlog, last updated in January 2026, says to open ChatGPT, then Settings, then Personalization, then Customize ChatGPT. The Mac Install Guide lists the same path as Application menu, Settings, Personalization, Customize ChatGPT. It also says the instructions are shared with the web browser version of ChatGPT. Text you save on the Mac is the same text you see in your browser.

Some screens label this section Custom instructions instead of Customize ChatGPT. A May 2026 TechSnaply post uses that wording. It describes two fields, a check that both contain text, and a toggle called Enable for new chats. If you see either label, you are in the right place.

What to write in the two fields

The fields are short, so spend your words on facts that change the answer. Say what you do and what you already know. Then say how you want answers shaped. Skip anything ChatGPT would guess anyway, such as a request to be polite. A good test is whether a new colleague would need the sentence to do the job well.

Write instructions that hold up

Short and specific beats long and vague. Be helpful tells ChatGPT almost nothing, because every answer is meant to help. A rule like show the full formula, then explain only the cells that changed tells it exactly what you want. Write rules you would give a new colleague on their first day. Then test them in a new chat and tighten the wording if the replies drift.

• Analyst: I work in Excel and SQL and know both well. Skip basics. Put formulas in code blocks.
• Newsletter writer: I write for a general audience in plain English. Give a few headline options when I ask. Keep sentences short.
• Student: I am studying biology for an exam. Explain ideas step by step. Ask one question before you give a final answer.

Character limits: 1,500 or 5,000 characters

The limit depends on your plan. LaunchReady reports that Free and Go accounts can save up to 1,500 characters of custom instructions. It says Plus, Pro, Business, Enterprise and Education accounts can save up to 5,000. The article ties the change to mid-July 2026 and cites OpenAI's Help Center, but it gives no exact date.

Treat those figures as reported, not confirmed. At the time of writing, OpenAI's own help pages could not be checked. A May 2026 TechSnaply post still says each field is limited to 1,500 characters, which conflicts with the paid figure. If your text is too long, trim it before you save. Count the characters in a text editor first.

Test that the instructions apply

Start a new chat after you save, because instructions apply to new conversations. Ask for something where the rules should show. A short summary in a fixed format works well. Compare the reply with what you wrote, and do not judge from one answer alone.

Say your profile says you are a data analyst who works in Excel. Your second field asks for short answers with bullet points. Start a new chat and ask for a summary of a sales table. If the reply comes back as bullet points with no greeting, the instructions are working. If it comes back as a long essay, check the toggle and the fields, then try again in a new chat.

Why the quick chat bar may ignore them

iGeeksBlog says the chat bar does not support these settings. That is easy to miss, because the chat bar looks like the rest of ChatGPT. Open a full chat window when you test. Use the chat bar for quick questions where your instructions do not matter.

Option+Space and the ChatGPT launcher

On Mac, Option+Space opens the ChatGPT launcher. The app must be running for the shortcut to work. The Mac Install Guide says you can change the shortcut in Settings. For more detail, read How to use the Option+Space shortcut in ChatGPT on Mac.

The new ChatGPT desktop app and AGENTS.md

The new app works differently. OpenAI's documentation for the ChatGPT desktop app, which it also calls Codex, says Settings opens from the app menu or with ⌘,. Under Personalization, you can turn on Enable Codex memories where that option exists. That toggle controls memories, not the text of your instructions.

The same docs say personal instructions are stored in AGENTS.md for the selected machine, and you edit them there. They give no full file path and no version number. So search in Settings first, then look for the file if you still need it. Keep the text plain and short, and save it before you open a new chat.

When new chats ignore your instructions

A May 2026 TechSnaply post lists fixes, roughly from the cheapest to the most involved. Start with the toggle. Switch Enable for new chats off, then on, and save. Move to the next fix only when the first one fails. The troubleshooting list below follows the same order.

Common mistakes to avoid

• Pasting a whole document. Long pasted text eats the limit and buries the rules that matter.
• Writing a task for today. Instructions apply to every new chat, so a one-off task belongs in that chat.
• Forgetting the toggle. If Enable for new chats is off, the text sits there and does not apply to new chats.
• Testing in the quick chat bar. iGeeksBlog says the chat bar does not support these settings.
• Assuming the Mac and web versions differ. The Mac Install Guide says they share the same instructions.
• Ignoring your plan limit. Free and Go accounts have less room than paid plans.

Requirements and menu paths at a glance

How to edit or turn off custom instructions

To change instructions, open the same screen, edit the text, and save. To stop them from applying, switch off Enable for new chats if your screen shows that toggle. Clearing both fields also removes them, according to TechSnaply. Save again, then start a new chat so you can confirm the change took.

What to do next

Use the instructions for a few days of normal work before you change them again. Change one line at a time, so you can see which edit made the difference. When you need to share a document in a chat, follow How to attach a file in ChatGPT on Mac.