Privacy policy
Prosper, by Silver Fern Labs · Last updated 6 July 2026 · Applies to the Android beta
The short version. Your health record lives in a database on your phone. We run no analytics, show no ads, and require no account. Nothing leaves your device unless you use the AI coach — and the coach only carries what you have explicitly, separately agreed to share. You can see, change, or delete everything, any time, in the app.
What the app stores — on your device
Prosper keeps its records in a local database on your phone:
- Your profile: age range, biological sex, height, weight, waist, dietary approach, goals, and (optionally) your shift roster.
- Health entries you log: fasts, meals, water, weight, glucose readings, blood pressure, resting heart rate, sleep, and any notes you choose to write.
- Data you sync from Health Connect, if you connect it (see below).
- Derived numbers the app computes for you: scores, trends, and modelled estimates — always labelled as such.
This data is not transmitted to us. We cannot see it. There is no cloud copy unless you export a backup yourself, and that backup goes where you put it.
Health Connect
If you choose to connect Google Health Connect, Prosper requests read-only access to exactly six record types: steps, sleep sessions, heart rate, resting heart rate, weight, and blood glucose. Synced values are stored in the same on-device database and follow the same rules as everything else. You can revoke this access at any time in Health Connect's settings.
The AI coach — the only thing that leaves your phone
Prosper's coach is powered by a large language model. When you send the coach a message, that message travels to a relay service we operate (on Cloudflare) and then to our AI provider (Anthropic) to generate the reply.
What travels with your message is under your control:
| Always included | Your message itself, recent conversation turns, and basic coaching context: your age range and biological sex. |
|---|---|
| Only if you switch on “Share health numbers” | Glucose, weight, body composition, score, fasting state, and roster pattern. |
| Only if you switch on “Share notes & coach memory” | Short facts the coach has learned about you between chats, and post-fast notes you write. |
Both switches are off by default. Before your first coach conversation the app shows you this list and asks for consent; declining leaves the whole coach feature off and nothing is sent. Conversations are processed to generate the reply and are not used to train AI models.
What we don't do
- No analytics or usage tracking of any kind.
- No advertising, no ad identifiers, no data brokers.
- No selling or sharing of personal information — there is nothing on our servers to sell.
- No account, no email list, no sign-up.
Deleting your data
Everything is yours to remove:
- Delete individual entries (a meal, a reading, a fast) directly in the app.
- “Reset & start over” in Settings wipes the entire on-device database.
- Uninstalling the app removes its database from your phone.
Because we hold no copy of your health record, there is nothing further for us to delete.
Children
Prosper involves fasting and metabolic health and is intended for adults aged 18 and over. It is not directed at children.
Your rights
We operate from New Zealand under the Privacy Act 2020, and we aim to meet the spirit of privacy law everywhere our users are (including the GDPR). Because your data stays on your device, the rights to access, correct, and delete it are built into the app itself. Questions, or anything you can't do in-app: email us and a human will answer.
Changes
If this policy changes in a way that matters — especially anything about what leaves your device — we will say so plainly in the app before the change applies to you, not bury it here.
Contact
Silver Fern Labs · Aotearoa New Zealand
hello@silverfernlabs.co.nz