Today's AI Tip
Tell ChatGPT about your job once. Then stop retyping it.
What you get without context
Real output · GPT-5.5 (OpenAI API) · Oct 2026
We asked for a caption for a 20% off sale, Oct 10 to Oct 19. It came back with 4 emojis, 2 exclamation marks and no mention of pickup.
Where the setting lives
Custom instructions are on all plans. Free and Go allow 1,500 characters; Plus, Pro, Business, Enterprise and Education allow 5,000. The diagram shows web and desktop; on mobile, use Settings → Customize ChatGPT.
Source: OpenAI Help Center, as of Oct 2026
The block to copy and adapt
Tested in GPT-5.5 (OpenAI API), Oct 2026
This is the block we tested for a fictional shop, Hollow Pine Candle Co. Swap in your own business, audience, voice and fixed rules.
Try it: Swap in your business, audience, voice and 2–3 fixed rules.
The same request, with context
Real output · GPT-5.5 (OpenAI API) · Oct 2026
Same sale, with the block: 42 words, no exclamation marks, free pickup and the end date. We pasted it into the message through the API, standing in for the app setting.
![When one rule overreaches. On a product launch, the same block produced "This promotion ends [end date]." The rule said every promotion, so it applied here. It also added scent notes we never gave it.](https://media.carouselcdn.com/ai-tools/2026-10-08-a/06.png)
When one rule overreaches
Real output · GPT-5.5 (OpenAI API) · Oct 2026
On a product launch, the same block produced "This promotion ends [end date]." The rule said every promotion, so it applied here. It also added scent notes we never gave it.
Give every rule a scope
Give each rule a scope: "On sale posts, say the end date." Check details the AI adds. Keep customer names, account numbers and personal details out, and check ChatGPT's data policy or your employer's approved tools.
Try it: To check your edit, start a new chat, rerun an old request, and compare.
Sources and assumptions
- OpenAI Help Center: ChatGPT Custom Instructions (read through the r.jina.ai reader because a direct fetch returned 403): Web & Desktop: 'In your Settings, select Personalization', toggle 'Enable customization', Custom Instructions field; iOS & Android: 'In your Settings, select Customize ChatGPT'; 'Custom instructions are available on all plans on Web, Desktop, iOS, and Android'; Free and Go up to 1,500 characters, Plus/Pro/Enterprise/Business/Education up to 5,000; 'There will be no API for custom instructions, as the Chat Completions API system messages should be used for a similar effect.' The page shows no last-updated date. (checked 2026-10-07)
- OpenAI API docs: GPT-5.5 model (per idea queue screen): GPT-5.5 is available in the OpenAI API; all four tests ran on model 'gpt-5.5' via engine/ai-test.js (checked 2026-10-07)
Assumptions:
- The tests ran through the OpenAI API (gpt-5.5, default settings: no reasoning_effort, temperature or system message set). The 'about my work' block was pasted at the top of the user message as a stand-in for the app's custom instructions setting. The ChatGPT app may add its own system prompt, so app results can differ.
- Hollow Pine Candle Co., its Asheville stall, prices, dates and Cedar Smoke are fictional sample material.
- Each test is a single run; outputs vary run to run.
- The help page contradicts itself on timing ('applied immediately across all chats (including existing conversations)' versus 'reflected only in future conversations'), so the post makes no claim about when changes take effect and tells readers to start a new chat to compare.
- The character limits and plan list are as of Oct 2026; the help page has no date, so slides say 'as of Oct 2026'.
The short version
- Write your business, audience and voice once
- Add two or three fixed rules
- Give each rule a scope
- Check details the AI adds
