Efferent encrypts every day of Apple Health on your iPhone and sends it to an archive that any AI agent can read on your behalf — ChatGPT, Claude, Gemini, or a script of your own. The key never leaves your phone until you choose to hand it over.
Steps, distance, energy, sleep, workouts, heart rate, heart rate variability, resting heart rate, respiratory rate, blood oxygen — every day since your first Apple Watch, as one sealed object per date.
New readings go up in the background as Health receives them. A watch that synced late, a workout you deleted a week later — the day is simply written again.
Each day is sealed on the phone with a key the phone created. The archive service stores ciphertext and can name a day and its size — never what happened in it.
Nothing to sign up for. The archive is addressed by a hash of your own reading key, and only your phone can write to it.
One prompt from the app gives an agent an MCP endpoint and a reading key. The agent fetches sealed days and decrypts them on its own machine.
The app, the wire protocol and the archive service are public on GitHub, so every claim on this page is one you can verify.
iOS cannot be a server: the phone is unreachable and asleep most of the time. So nothing ever connects to your phone. The phone pushes, and the meeting point lives elsewhere.
Efferent reads whatever you tick in the Health permission sheet. You can change it any time in Health → Apps and Services.
The phone makes a reading key and a signing key, claims a place for the sealed days, and starts sending — the whole history first, then each new day by itself.
Tap Connect and share one prompt with the agent you use. It says where the archive is, what opens it, and what to do first.
"How did my sleep change since I started running?" The agent lists the days it needs, decrypts them locally and answers. Your phone can be off.
Encryption hides contents, not the fact of them, so this is said plainly. The service learns which days exist, how large each sealed day is and when it was written. It does not learn what kind of readings a day holds, at what hour, or of what value — all of that exists only after decryption, on the machine holding your reading key.
phone ──sealed days──▶ archive (Cloudflare R2) agent ──MCP──────────▶ listing and sealed days agent + reading key ──▶ decryption and answers, on the agent's machine
Efferent is a one-time purchase on the App Store. Requires an iPhone with iOS 17 or later and Apple Health.
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