# What you can and can't build with ChatGPT or Claude

"Build me an app" is an easy thing to ask ChatGPT or Claude. Some of those requests turn into a real working app. Others look finished but can't do the thing that matters.

This is where the line sits when you build from a chat with Toupas, and what to do when you reach it.

## What works well

Chat-built apps are good at one pattern: **people save things, and rules decide who can see them.**

- RSVP lists and waitlists
- Guestbooks
- Simple customer lists
- Team trackers
- Member directories

Each of these gets sign-in by email code, its own database, access rules for each list and even each field, and an admin page. The rules are enforced on the server, so hiding something on the page isn't what protects it.

## What it can't do

These apps have no custom code running on the server. The chat describes your data and rules, and a fixed backend does the rest. So they can't do any of this:

| You want | Why it doesn't fit |
|---|---|
| Take payments | Needs a secret key and code to confirm the payment |
| Receive webhooks | Nothing custom can run when another service calls in |
| Keep secret API keys | The page runs in visitors' browsers, where anyone can read it |
| Run scheduled jobs | Reminders on a timer need code running on the server |
| Call an AI model | Needs a secret key, so the same problem applies |
| Apply custom business rules | "Only allow 50 bookings", enforced on the server, is beyond the access rules |

The last one catches people out. A chat may write that check in the page, and it'll look right. But a limit that only exists in the browser can be bypassed, so treat it as a convenience and not as a real rule.

Which leads to the point worth remembering: **a chat can make something look like it does a thing it doesn't do.** Test what matters. Sign in as a different person, and try to do what you shouldn't be able to.

## Practical limits

Even inside that pattern, there are some numbers to know:

- **Memory.** Each chat-built app runs on its own and uses 128 MB. That's all the memory the App plan includes, so a second always-on app needs more memory added to your plan.
- **Sign-in emails.** Up to 60 an hour per app on a plan, and 20 on a free trial.
- **Size.** Each update can carry up to 2 MB of files, so large images should be hosted elsewhere and linked.
- **Backups.** Nightly, to a separate place. You could lose up to a day of changes if something goes badly wrong, so download anything important from the admin page.

Plain websites have no server of their own, so they don't use memory like this. They fit on the cheaper Website plan.

## When you reach the line

Say your waitlist has grown, and now you want to charge for a place. You have two options.

**Move the app to code.** From the Toupas panel, you can get the whole app as ordinary code, then open it in an editor with a coding agent. Your data, your users and your links stay as they are.

Before you do, know that **this is one-way.** Once you make that code live, chats can no longer update the app, and you can't undo it. Downloading the code to look at it changes nothing, so you're free to look first.

**Start in code.** If you know from day one that you need payments or an AI feature, skip the chat and [use a coding agent](/agents) from the start. You'll avoid doing the move later.

## A quick way to decide

![If nothing is saved, make a website from a chat. If people save things, make an app from a chat. If money, AI, timers or custom rules are involved, use a coding agent.](/blog/images/what-to-build-with.svg)

- **Only information, nothing saved?** Make a [website from a chat](/blog/deploy-website-from-chatgpt-or-claude).
- **People save things, and it matters who sees them?** Make an [app from a chat](/blog/build-rsvp-app-with-chatgpt-or-claude).
- **Money, AI, timers or custom rules involved?** Use a [coding agent](/blog/deploy-claude-code-app).

We'd rather you found this out here than after building the wrong thing. If you're unsure, describe your idea in the chat and ask it directly: "Which parts of this can't a Toupas chat app do?"

## Questions

### Can ChatGPT or Claude build an app with a login?

Yes. With Toupas added to your chat, you can describe an app with email sign-in and saved data, and it goes live at a link. You choose who can see what.

### Can an app built in a chat take payments?

Not directly. Payments need a secret key and custom server code, so you'd move the app to code first, or start with a coding agent.

### Can the chat see what people save in my app?

No. It can see the shape of your data and how many rows there are, but not the rows themselves. You see those on the app's admin page.

### What happens if my app outgrows the chat?

You can move it to ordinary code, and your data, people and links stay as they are. Once that code is live, chats can't update the app, and you can't undo that.