Last updated: May 8, 2026

Onyx is built on a simple privacy stance: your health data stays on your phone, except for the one feature that needs to leave it. This policy explains exactly what we do, what we don't do, and what you can control.

What stays on your phone

Almost everything. Your workouts, food log, saved recipes, recovery scores, sleep notes, profile, and settings are all stored in your device's local database. There is no Onyx-side login. We don't run a server that holds your account data. If you delete the app, that data is gone.

What we read from Apple Health

With your permission, Onyx reads a small set of metrics to compute your daily recovery score and spot illness early-warning patterns:

• Heart rate variability (HRV)
• Resting heart rate
• Sleep stages and duration
• Steps and active energy
• Exercise minutes
• VO₂ max
• Respiratory rate
• Wrist temperature deviation
• Body mass, body fat, and waist circumference

We don't read anything else. The full list lives in Settings → Privacy → Health → Onyx on your iPhone, where you can revoke any individual metric at any time.

What we write to Apple Health

• Completed workouts, so they appear in the Fitness app and close your Activity rings
• Body mass, body fat, and waist measurements you log inside Onyx

Manual nutrition logs are not written to Apple Health.