The spectrum of who can read your data
Every storage product sits somewhere on one line: who, besides you, could read this? At one end sits ordinary cloud storage — encrypted "in transit and at rest", but with keys held by the provider, so the provider (and anyone who compels or compromises it) can read everything. In the middle sits zero-knowledge: your device encrypts before upload, the provider stores ciphertext it cannot open. At the far end sits local-first: the data never becomes a provider's copy at all.
What zero-knowledge actually promises
In a zero-knowledge design, your password never leaves your device; keys are derived locally, content is encrypted client-side, and the server sees only ciphertext. Done honestly, this is a real and meaningful guarantee: a breach of the provider leaks gibberish, and the provider cannot be forced to produce plaintext it cannot make.
But notice what survives: the provider still knows you — your account, your email, your payment trail — and still knows that you store data, roughly how much, and when it changes. Ciphertext plus identity is not nothing; it is a map of where the secrets are, with your name on it.
The recovery-path test
One question cuts through most marketing: "What happens if I forget my password?" If the answer is "we can help you get back in", then a path to your data exists that doesn't run through you — and whatever that path is, it can be used, breached, or compelled. If the answer is "we can't help; only your recovery phrase can", you're looking at the real thing. Inconvenient answers are how you recognise honest cryptography.
One step further: no provider at all
Sealby's answer to "what can the provider see?" is structural: there is no provider in the loop. No account identifies you, no server stores your ciphertext, and encryption happens on your iPhone with keys in the Secure Enclave. If you enable backup, the blob goes to your iCloud — still unreadable to Apple and to us. Each vault has its own recovery phrase, and losing it means no one can help — which is precisely the property everything else here has been circling.