How to build an app like ChatGPT
Almost nobody searching for this wants to build another ChatGPT. What they want, nearly always, is an assistant for one subject: one that knows your catalogue, your rules, your documents, and talks to your customers.
That version is viable, and it is the only one that makes economic sense.
What you can build
- a conversation screen with per-user history, the one everybody already knows how to use;
- an assistant with a personality and rules, defined by you in plain text;
- your documents as the source: price list, policy, manual, catalogue;
- user accounts, so you know who said what and conversations stay separate;
- limits, which here are not a detail: they are what keeps the bill from exploding.
The three things that decide the result
1. The instructions. They are what turns a generic model into your assistant: what it does, what it never does, how it answers when it does not know. They are worth more than any technical tuning.
2. The context. The assistant is only good on your subject if it receives your material alongside the question. Organised documents beat voluminous ones.
3. The limit. With no per-user daily cap, one curious person spends the month's budget in an afternoon.
The cost behaves unlike any other app
Here you pay per message, and the price rises with the length of the conversation, because the history is resent with every question. It is the line that surprises people coming from other projects.
Three measures handle it:
- a daily message cap per user;
- trimming the history after N exchanges;
- an assistant that answers briefly by default, and at length only on request.
What does not come ready
- training your own model. It is not what most people need, and instructions plus context almost always solve it better and cheaper;
- a guarantee that it never gets things wrong. No assistant has one. What you can do is show the source and leave a path open to a human;
- automatic moderation of what users write. If the app carries conversation, the stores require a way to report and to block.
A prompt to start with today
A chat app with an assistant that answers questions about [your subject]. Each user has an account and sees only their own conversations. The assistant follows these rules: [three rules], and when it does not know, it offers to put the person in touch with our team. Each user can send up to [N] messages a day.
The summary
- the viable app is not another ChatGPT, it is the single-subject assistant;
- instructions, context and limits decide the result, in that order;
- the cost is per message and grows with history: trim the history;
- training a model is almost never the answer;
- conversation between people needs reporting and blocking to pass store review.
A ready request to build your own
Build an AI assistant app for dietitians to use with their patients. The patient logs in with their own account and chats with the AI about the meal plan the dietitian set up for them, asking about substitutions and portions; the AI answers only based on that plan and tells the patient to contact the dietitian when the question is clinical; a limit of 20 messages per day per patient; chat history is saved; the dietitian sees their patients' conversations and edits the plans; and an admin dashboard only I can see with active patients, messages per day and the month's AI cost.
Free to start. The first version arrives in a few minutes and you refine it by chatting.