I built a local-first Apple Health archive that agents can read via CLI/MCP

Hi everyone — I’m building Nucleus, a local-first personal data archive that starts with Apple Health.

The idea is simple: personal data should outlive the app that captured it. Health data, notes, calendar context, and other personal records are usually trapped inside apps, cloud dashboards, or exports that are hard to inspect or reuse. I wanted a more durable default: private by default, structured, readable by humans, and usable by local tools or agents.

The first release focuses on Apple Health. With the user’s permission, the iOS app creates local Health exports first. No account is required, and it is not trying to become another hosted sync product.

What it supports today:

- daily Health exports with a predictable structure

- raw sample history

- incremental background refresh

- widgets / Live Activity status surfaces

- optional upload to a user-owned S3-compatible bucket

- CLI and MCP access over the same exported archive

The part I’m most interested in is the agent-readable layer. The CLI and MCP server can read the same exported archive, so tools like Claude Code, Codex, or other MCP clients can reason over private structured data without the app becoming the center of everything.

Example use cases I’m testing:

- morning briefs using sleep/recovery + calendar context

- weekly reviews across health trends and working notes

- long-range archive queries over personal data

- meeting prep that uses schedule + notes + current energy context

This is not meant to be an AI health coach or medical advice tool. The goal is infrastructure: a quiet archive that keeps personal data private, structured, durable, and useful outside the original app.

I wrote more about the architecture and first release here:

https://zish-rob-crur.com/blog/introducing-nucleus/

Github
https://github.com/zish-rob-crur/nucleus-apple-mcp

I’d love feedback from people who care about local-first software, personal data ownership, MCP, or self-hosted workflows:

- Does this archive shape make sense?

- Would you trust optional S3-compatible storage for agent access?

- What personal data domains should come after Apple Health?

- What would make this useful enough for your own workflow?