How to use a system prompt in ChatGPT
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ChatGPT has several places to put standing instructions. They differ in how much text they hold and which chats they apply to. The prompts on this site are between about 9,000 and 25,500 characters long, with most around 14,000, so the field you choose decides whether a prompt fits whole. For how the prompts are structured, see How to use the prompts on this site.
Projects
A project groups chats, files and instructions. Project instructions apply to every chat in that project. OpenAI's help centre says projects are available to signed-in users, subject to plan availability and workspace settings.
- Select New project in the sidebar.
- Enter a name, then choose an icon and colour.
- In the project, open the more options menu (•••) and select Project settings.
- Paste the prompt into the instructions and save. Delete the closing label and bracketed slot, such as
[REQUEST], first. - Start a chat inside the project and type your request.
Project instructions apply only within that project and override your global custom instructions. OpenAI's help article does not state a character limit for project instructions.
You can also add the prompt to the project as a file: projects accept uploaded documents and pasted text. Use the Raw .txt link on any prompt page to get it as a text file. The number of files per project depends on plan:
| Plan | Files per project |
|---|---|
| Free | 5 |
| Go, Plus | 25 |
| Pro, Business, Enterprise, Edu | 40 |
Up to 10 files can be uploaded at the same time.
Custom instructions
Custom instructions apply to all your chats. On the web and desktop:
- Open Settings and select Personalization.
- Make sure Enable customization is on.
- Enter text in the Custom Instructions field.
On iOS and Android, the setting is under Settings, then Customize ChatGPT.
The character limits are:
| Plan | Custom instructions limit |
|---|---|
| Free, Go | 1,500 characters |
| Plus, Pro, Business, Enterprise, Education | 5,000 characters |
No prompt on this site fits in either limit. The shortest is about 9,000 characters, and a typical one would need to lose around two thirds of its text to fit in 5,000. To use one here you would have to trim it heavily; the trimming section of How to use the prompts on this site describes how. Because custom instructions apply to every chat, a role-specific prompt placed here also affects chats that have nothing to do with that role.
GPTs
OpenAI is retiring custom GPTs and moving them to plugins. Its help centre gives these dates:
- New GPT creation and publishing are already unavailable on personal accounts, including Free, Go, Plus and Pro. Business, Enterprise and Edu workspaces can create GPTs where workspace settings allow.
- Creation of new custom GPTs is planned to end on Oct 26, 2026.
- Custom GPTs are scheduled to retire on Dec 11, 2026, when GPTs and their pages become inaccessible. Some Enterprise workspaces with an approved deferral have until Feb 11, 2027.
When a GPT is migrated, its instructions become a skill within a plugin and its knowledge files are copied into the plugin's reference files. OpenAI's skills article says skills are available to eligible Business, Enterprise, Healthcare and Edu users.
If you can still create or edit a GPT, the steps are:
- Open Explore GPTs in the sidebar, or go to chatgpt.com/gpts. GPT creation works on the web only.
- Select Create, then use the configuration view to edit the fields directly.
- Paste the prompt into Instructions, without the closing slot.
- Under Knowledge, upload files if needed. A GPT can have up to 20 files, each up to 512 MB.
- Test it in Preview, then select Create or Update.
OpenAI's current GPT article does not state a character limit for the Instructions field. If the editor does not accept the full prompt, one approach is to upload the prompt as a knowledge file and write a short instruction telling the GPT to follow it. OpenAI's guidance says knowledge is meant for reference material and that rules and tone belong in Instructions, so behaviour may differ from having the whole prompt in Instructions.
Pasting into a chat
This works on any plan and in any chat:
- Open the prompt page and select Copy prompt.
- Start a new chat and paste.
- Replace the bracketed slot at the end with your request and any material, then send.
The instructions apply for the rest of that chat. A new chat starts without them.
The OpenAI API
In the Responses API, put the prompt in the instructions parameter and the user's request in input. OpenAI's documentation says instructions given this way take priority over the prompt in input. The instructions parameter applies only to the current request: if you continue a conversation with previous_response_id, instructions from earlier turns are not carried over, so send them again with each request.
You can also send the prompt as a message with the developer role, which OpenAI describes as instructions from the application developer, prioritised ahead of user messages. In the Chat Completions API, developer messages replace the earlier system messages for newer models.
There is no API for ChatGPT's custom instructions; OpenAI points developers to system and developer messages instead.
Sources
Menu names and labels in ChatGPT change from time to time. These are the official pages used for this guide, checked on 2026-10-03: