ChatGPT Custom Instructions and Claude: A Practical Guide
ChatGPT custom instructions and Claude explained: what they are, how to write a reusable starter prompt and use it safely on shared accounts.
ChatGPT custom instructions, and similar features in assistants like Claude, are preferences you write once so the assistant applies them to its replies: your field, preferred language, answer length and tone. The point is to stop repeating the same briefing at the start of every chat. This guide shows how to write them well, and how to get the same benefit safely when you work on a shared account without affecting anyone else.
What Are Custom Instructions and Why Do They Matter?
Every new chat starts with no idea who you are. If you write casual Egyptian Arabic for a young audience, you would otherwise have to say so every time. Most major assistants offer a settings area for persistent instructions, with different names: custom instructions in ChatGPT, project level instructions in Claude, and custom assistants in Gemini. Names and locations can change with updates, but the principle is the same: fixed text the assistant reads before replying.
- Replies in your style from the first message.
- No retyping the same background.
- More consistent results on repeat tasks.
- Fewer long, padded introductions.
An Important Warning for Shared Accounts
If you use ChatGPT or Claude through shared access like the kind ZTOOLZ provides, the account belongs to the platform and other people use it too. Changing account wide settings, such as custom instructions, memory or language, can change the tool's behaviour for others, and their changes can affect you.
On any shared account, do not edit custom instructions or account settings, and do not store personal information anywhere. The safe alternative is a personal starter prompt saved on your device and pasted at the start of each chat.
You get almost the same benefit, because the assistant follows instructions from the first message for the whole conversation. For more habits, read security habits for shared accounts.
How Do You Write Great Instructions or a Starter Prompt?
Answer two questions: who you are and what you work on, and how you want replies. Keep it short, since very long instructions can conflict.
- Describe your field without personal data.
- Name your audience.
- Set language and tone.
- Set reply format: brief or detailed, bullets or prose.
- List what to avoid: long intros, clichés, invented numbers.
- Test for a week and adjust.
Write as if you were briefing a new assistant on their first day. Plain, direct sentences work better than elaborate descriptions.
Ready Templates by Role
Content creator
I write tech posts and video scripts for Arab viewers aged 18 to 30. Use light Egyptian Arabic unless I ask otherwise. Short, direct sentences, no intros, no clichés. When I ask for ideas, give 10 varied options. Never invent statistics.
University student
I study engineering. Explain concepts in Arabic with English technical terms in brackets. Start with a simple example. When I am solving a problem, give a hint first and wait for my attempt.
Developer
I mainly use PHP and JavaScript. Write complete, runnable code with brief comments. Keep my variable names. Show the simplest solution first and mention alternatives in one line. Flag any security issue.
Customer support
I write replies for an online store. Polite, warm and brief. Acknowledge the problem, give the solution, then one clear next step. Never promise anything not in the information I provide.
How Do You Use a Starter Prompt Well?
Keep versions for writing, studying and coding in a notes file. Paste the right one at the start of a chat and add your task below it. If a long chat drifts, remind it: "Please follow the instructions at the top of this chat," or start fresh. To improve the content of your instructions, use our prompt writing frameworks.
Signs your instructions need an update
- You keep typing the same correction.
- Replies are consistently too long or too short.
- One instruction is ignored, often because it is unclear or conflicts with another.
- Your work has changed.
Common Mistakes
- Conflicts, such as "be brief" and "explain in detail".
- Padding unrelated to your tasks.
- Personal data the assistant does not need.
- Vagueness: "write well" is not an instruction.
- Editing a shared account's settings, the most important one to avoid.
ZTOOLZ offers shared access to AI chat tools through the Chrome extension, the ZTOOLZ secure browser or cloud tools depending on the tool, and the line up changes. Check the store.
FAQ
Where are custom instructions in ChatGPT?
Usually in the settings or personalisation menu, though placement can change. On a shared account, leave them alone and use a starter prompt.
Does Claude support custom instructions?
Claude supports persistent instructions in different forms, such as project level instructions. A starter prompt works with any assistant.
Custom instructions vs a normal prompt?
Custom instructions apply to every chat automatically; a prompt applies only to its chat. A starter prompt is the practical middle ground for shared accounts.
How long should instructions be?
Five to ten clear lines is usually enough, as long as nothing conflicts.
