Where is my key stored, and who can see it?

In your browser's local storage, on the machine you typed it on. It is deliberately excluded from the settings that sync between your devices, so it never reaches our database. Nobody at TradePerformance can see it, because we never receive it.

The key lives under one storage entry in that browser and goes nowhere else.

It does not sync, on purpose. The settings sync mirrors your preferences to your account row so they follow you between devices. The key is excluded by name, and there is a test in the codebase whose only job is to fail the build if anyone adds it back. The reason is blunt: the sync mirror is not encrypted, and a provider key is your money.

Two consequences worth planning around. If you use the app on a laptop and a desktop, paste the key on both. And clearing that browser's site data removes it — you will need to paste it again.

Where it goes when a feature runs: straight from your browser to the provider's API, over TLS, as the authorization header on that one request. It is not sent to us, it is not included in any export, and it is not written into your trades.

The banner above the provider list says the same thing, and it is worth reading once: the key is stored in that browser, never uploaded, never logged, never sent to a third party, and clearable with Remove whenever you like.