Setting it up in your tool

This is the payoff lesson. Everything you drafted in lessons 2 through 4 is sitting in a notes app. Ten minutes from now it will be installed in the tool you use every day, and every chat you start will already know your business, your voice, and your rules.

One honest warning before the steps. Menu names in these apps change every few months. Everything below is accurate as of August 2026, and the concepts will outlast the labels. If a button has moved, look for the words instructions, personalization, project, or Gem, and you will find it.

Three tools, two designs

The three big apps take two different approaches, and it helps to know which is which before you start.

ChatGPT's custom instructions are account-wide. You write them once in settings and they apply to every chat you start, about anything. That is simple and powerful, but it means one prompt has to fit all your uses. If you use ChatGPT for both your gutter business and your kid's science project, the science project gets the gutter voice.

Claude Projects and Gemini Gems are per-workspace. You create a named container, put the system prompt inside it, and only chats started inside that container use it. You can have one for the business, one for personal stuff, one for a specific client. The cost is one extra tap: you have to pick the project or Gem before you start chatting. Both Claude and Gemini also let you attach files (a price list, a brand guide) that the assistant can reference, which the Documents and Data module covers.

Neither design is better. Account-wide is right if you mostly use the tool for one thing. Per-workspace is right if you wear several hats. As of August 2026, Claude also offers an account-wide instructions setting in addition to Projects, so you can combine the two: general preferences at the account level, business specifics in a project.

Step by step for each tool

Pick your tool below and tap each step as you finish it. Do it on a laptop if you can; the phone apps have the same features but the settings are buried one menu deeper.

What to know about each one

ChatGPT. Custom instructions live under Settings, then Personalization. There are two boxes. "What would you like ChatGPT to know about you?" is for the role, audience, and goals blocks. "How would you like ChatGPT to respond?" is for persona, format rules, boundaries, and your voice sample. The split is a little arbitrary, and the model reads both together, so do not agonize over which box a sentence goes in. Custom instructions are available on every plan, including free. The catch is length: free and Go accounts get 1,500 characters, while paid plans (Plus and up) get 5,000, a limit that was raised in July 2026. A 300-word system prompt is roughly 1,800 characters, so on a free plan you will likely need to trim. Watch the counter under each box as you paste. Once saved, new chats pick it up immediately.

Claude. Projects are available on every plan as of August 2026, with free accounts capped at five projects and paid plans unlimited. Create a project, open it, and find the box for project instructions. Paste the whole system prompt there, headings and all. There is no published character limit that we could verify, but the same advice applies: shorter is read more carefully. The thing to remember with Claude is that the instructions only apply to chats started inside the project. If you start a chat from the main screen, you get default Claude. Make a habit of opening the project first.

Gemini. Gems are Google's version of a project. On the web, look for Gems in the left sidebar (the link is labeled Explore Gems as of August 2026), then New Gem. Give it a name, paste your system prompt into the Instructions box, and use the preview pane on the right to ask a test question before you save. Google's own guidance for that box asks for persona, task, context, and format, which maps neatly onto the six parts from lesson 2. Gems can be created on the free Gemini plan, though some of the tools a Gem can use may depend on your plan. Like Claude, you have to pick the Gem before you chat.

Keeping more than one

Most owners end up wanting two or three system prompts once they see how well one works. A marketing voice for posts and reviews. A straight, careful voice for quotes and emails. Maybe an expert persona from lesson 3 for diagnosing problems in the field.

In Claude and Gemini this is natural: one project or Gem per job. Name them by the job, not the tool ("Review replies," not "Claude prompt 2"), because six months from now you will not remember which was which.

In ChatGPT, custom instructions are one set per account, so the usual move is to keep the account-wide instructions general (who you are, your voice, your boundaries) and put job-specific detail in the first message of each chat. ChatGPT also has its own per-workspace features that can hold separate instructions, and they change often enough that we will not walk through them here. If you find yourself wanting several distinct setups in ChatGPT, that is the feature to look for in the sidebar.

Whichever tool you use, keep the master copy of every system prompt in your own notes, not only inside the app. Apps lose settings, accounts get reset, and you may switch tools. The prompt is yours. The app is just where it currently lives.

On your phone

All three apps have the same features on iPhone and Android, and once your prompt is installed it works identically on every device signed into the same account. Setting it up on the phone is just fiddlier. In each app, the entry point is your profile picture or initials, usually in a corner of the screen, and from there the same words apply: personalization, projects, Gems. If you are pasting a long prompt, do it once on a laptop and let it sync. If you only have a phone, write the prompt in your notes app first so you are not composing inside a small settings box, then copy and paste it in.

Try this yourself

Install it now. Take your assembled prompt from lessons 2 through 4 and follow the checklist above for your tool. If you are on a free ChatGPT plan and over the limit, use this compressed shape, which lands under 1,500 characters for most businesses when you fill in the brackets.

Box 1: What would you like ChatGPT to know about you?
I own [business], a [what you do] in [city], Utah. Customers are [who]. I use you for [job 1], [job 2], [job 3]. My voice: [three or four short rules from lesson 3]. Sample of my voice: "[one real sentence]."

Box 2: How would you like ChatGPT to respond?
Under [N] words unless I ask for more. Plain sentences, no bullet lists in customer-facing text, no hashtags, no emojis, no exclamation points. Never state a price, date, or warranty term; say a quote needs a site visit. Never give legal, medical, or safety advice. Only state facts about my business that I have told you. If you are missing a detail, ask me one question instead of guessing.

Save it, open a brand new chat, and type just: "Who am I and what do you do for me?" If the answer reads back your business and your rules, you are installed. If it does not, go back and check the scope. Then move on to lesson 6, where you will test it properly. If you skipped the drafting lessons, the template in lesson 2 gets you a usable first draft in ten minutes.