Treat AI-generated code like code from any stranger: it can have bugs and it can do more than you expected. Running it in an isolated sandbox — as CanvasRunner does — contains the blast radius. Still read what it does before you trust it with anything that matters.
An AI assistant will happily write you a working app in seconds. That speed can make it feel safe, which is the wrong instinct. The right instinct is the one you would apply to a script a stranger handed you: what can this actually do?
The real risks
There are two, and they are different.
Bugs. The app miscalculates, loses your data on reload, or crashes on an input the assistant did not think of. Annoying, not dangerous. This is by far the common case.
Overreach. The app does something you did not ask for — makes network requests, reads more than it needs, or includes code copied from somewhere with a problem in it. Rare in a small single-file app, but not impossible, and worth guarding against.
What a sandbox does
CanvasRunner runs each app in an isolated local sandbox. Concretely:
- Each app gets its own origin, separate from every other app and from CanvasRunner itself. One app cannot read another's storage.
- The app runs against local files. You can watch every request it makes in the Inspector's network log and see which were served locally and which tried to reach out.
- Device permissions — notifications, vibration, location — are asked for at the moment the app calls for them, the same as in a browser, and that data stays on the device. CanvasRunner itself collects nothing.
A sandbox does not make bad code good. It makes the consequences of bad code small and visible.
Sensible habits
- Skim the code. For a single-file app it is a few hundred lines. You do not need to understand all of it — look for network calls and anything that looks out of place for what you asked.
- Watch the network log on the first run. A trip planner that phones home is a red flag.
- Keep the important copy elsewhere. If the app holds something you cannot lose, that data should also live somewhere you control. Backup in CanvasRunner helps it survive a new phone, but it is not your system of record.
- Throw it away when you are done. A personal app has a short life by design. Fewer old apps sitting around is less to think about.
The honest summary
Running a small app an assistant wrote, in a sandbox, on your own device, for your own use, is low-risk — lower than installing a random free app from a store, which runs with far more access and which you cannot read. The failure you will actually hit is a bug, and the fix for that is the Copy fix prompt loop, not a security incident.