Marrow vs MetricBridge: free on-phone MCP, or a zero-dependency local server
Two ways to let an AI read your Apple Health data without a cloud account. Marrow is free: an iOS app that exposes seven read-only MCP tools over Streamable HTTP on your local network, plus an optional self-hosted Python mirror that keeps a SQLite copy so the agent works with the phone in your pocket. MetricBridge is a $24.99 one-time unlock: the app writes 190 metrics to a JSON file, and a zero-dependency Node server reads them over stdio.
The honest split:
- Cheapest and agent-first setup: Marrow, and it is not close.
- Reach from any host, no LAN or token to manage: the stdio path wins.
- Native meal and weightlifting logs: Marrow already has them.
- An on-device ask-your-data layer with provenance: MetricBridge.
The part people miss: Apple's platform security rules put HealthKit in the Protected Unless Open class, and access is relinquished 10 minutes after the device locks. No local design escapes that. An on-phone server fails the call. A mirror or a file serves the last sync instead. Pick the failure mode you can live with.
Full comparison, including install shapes and the freshness check: https://dub.sh/yzx84en
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