shaughv-health-mcp

A private, single-user remote MCP server on Vercel that lets Emmett's trusted LLM assistants — Claude Code / Claude Desktop, claude.ai (web + mobile connectors), and ChatGPT connectors — read his Google Health / Fitbit Air data ("How many steps today?", "How did I sleep?", "Why am I tired?", "What did I eat yesterday?") and write the things a Fitbit Air can't track itself: nutrition, hydration, and body measurements.

It is a thin, typed, authenticated data adapter over the Google Health API (health.googleapis.com/v4). The LLM does the reasoning; this server returns accurate data with timestamps, units, and freshness metadata on every response. It is not a health warehouse, an analytics product, or anything that diagnoses — there are no medical claims anywhere in the surface.

docs/PLAN.md is the build plan and the source of truth for architecture, the four auth layers, the database schema, the tool surface, the watchouts, and the E2E verification bar. This README is the human front door; the plan governs the build. Live phase/task status is on the .tasks/ board — see Task board.

Table of contents

• What it is / what it is not

• Who it's for and how it's used

• Architecture

• The four auth layers (never conflate)

• Tech stack

• Current status

• Repository structure

• Setup guide

  • 1. Accounts and services

  • 2. Google OAuth redirect URIs

  • 3. Environment variables

  • 4. Local development

  • 5. Deploy

• Connecting an MCP client

• MCP surface

• Security posture

• Troubleshooting

• Task board

• Further reading

Related MCP server: Google Health MCP

What it is / what it is not

The device data path is never live — a Fitbit Air syncs to the Fitbit app, which pushes to the Google Health cloud, which this server reads on demand. Every response therefore carries freshness metadata (retrievedAt, latestDataTime?, isPossiblyStale, note) so the LLM can distinguish "no data synced yet" from "nothing happened."

Who it's for and how it's used

Audience: Emmett, and the LLM assistants he authorizes. Nobody else can sign in (sign-in is locked to ALLOWED_GOOGLE_EMAILS).

Intent — how Emmett uses it. He asks his assistants natural questions and expects grounded answers with real numbers, timestamps, and freshness notes:

• "How many steps do I have today? What's left to hit my goal?"

• "How did I sleep last night?" / "Why am I tired?"

• "Why is my heart rate so high?" (latest synced HR, explicitly not live)

• "What did I eat yesterday?" / "What's my exercise looking like this week?"

• "Log a snack: Greek yogurt, 150 cal, 15 g protein." / "Edit that to 180 cal." / "Delete it."

• "Log 16 oz of water." / "Update my weight to X."

Writes are the reason the server exists at all beyond read-only: a Fitbit Air does not track food, water, or manual measurements, so the LLM logs them through validated, audit-logged write tools. Every mutation is explicit-input-only (never inferred) and leaves an audit row.

Future directions (parked on the board, not part of v1 — see Task board):

• #api — a plain REST API surface (bearer/PAT-authenticated) over the same health services, so Emmett's own scripts/apps can call the data without an OAuth dance. Feasibility analyzed: feasible and additive on the current stack.

• #rlw — a possible future migration from Vercel serverless to Railway (long-lived container); this is the moment the FastMCP question reopens.

• #w11 — v1.1 webhooks: learn when new data lands (subscriber registration, signature verification, a freshness ledger). Deferred by design; tables already exist but stay dormant in v1.

Architecture

                    ┌─────────────┐   Bluetooth sync   ┌──────────────┐
   Fitbit Air ─────▶│  Fitbit app  │ ─────────────────▶│ Google Health │
   (wearable)       │  (phone)     │                    │    cloud     │
                    └─────────────┘                     └──────┬───────┘
                                                               │  Google Health API
                                                               │  health.googleapis.com/v4
                                                               │  ▲ user OAuth token
                                                               │  │  (AES-256-GCM
                                                               │  │   encrypted in Neon)
                                                               ▼  │
   ┌───────────────────────────┐   OAuth 2.1 + DCR    ┌────────┴──────────────────────┐
   │  LLM client               │ ───────────────────▶ │  Next.js on Vercel            │
   │  Claude Code / Desktop    │                       │  (health.emmetts.dev)         │
   │  claude.ai web + mobile   │ ◀─────────────────── │                               │
   │  ChatGPT connector        │   MCP tools/resources │  ┌─────────────────────────┐  │
   └───────────────────────────┘                       │  │ mcp-handler  → /api/mcp │  │
                                                        │  │ better-auth  → OAuth AS │  │
                                                        │  │ Google Health client    │  │
                                                        │  └───────────┬─────────────┘  │
                                                        └──────────────┼────────────────┘
                                                                       │ Drizzle ORM
                                                                       ▼
                                                             ┌──────────────────┐
                                                             │  Neon Postgres    │
                                                             │  encrypted tokens │
                                                             │  audit log        │
                                                             │  webhook tables   │
                                                             │  (dormant, v1.1)  │
                                                             └──────────────────┘

Request path in one line: an LLM client completes an OAuth 2.1 flow (with Dynamic Client Registration) against this app's own authorization server, gets a token, calls the MCP endpoint; a tool handler resolves the app user, fetches fresh data from Google Health using the decrypted-on-demand health token, bounds/normalizes the payload, and returns it with freshness metadata.

The four auth layers (never conflate)

These are four separate things. Confusing them is the number-one source of bugs here.

Layers 3 and 4 use the same Google OAuth client ID but separate flows and scopes. Layer 4's login uses basic openid email profile scopes only; layer 3 requests the nine googlehealth.* scopes. The health-flow refresh token is the one that gates data access.

Tech stack

Current status

Milestone #v1 (target 2026-07-16). The .tasks/ board is the live source of phase status; this section is a coarse snapshot that intentionally avoids fast-moving detail.

• Done and verified on prod: repo bootstrap, operator infrastructure (Vercel project live on health.emmetts.dev, Neon connected, Google OAuth client wired with all six redirect URIs, app published to production), the database + security foundation (encryption, redaction, audit, all 15 tables migrated), and MCP client auth (better-auth OAuth 2.1 + DCR, Google sign-in locked to the allowlist — live sign-in confirmed on prod).

• Landed / wrapping up: the Google Health consent + token lifecycle flow (health-scope consent, encrypted token store, identity mapping, single-flight refresh) — deployed to prod, awaiting Emmett's one-time health-consent click test — and the typed Google Health API client (data-type registry, request methods, error normalization, Luxon time utils).

• Pending: the MCP endpoint + read tools + resources (Phase 5), write tools + audit (Phase 6), and the deploy/wire-clients E2E acceptance run (Phase 7).

• Check the board for exact state — phases are moving daily; .tasks/TASKS.md is authoritative.

• Deferred by design: Google Health webhooks (v1.1, #w11).

The MCP endpoint (/api/mcp) is not live yet — it lands in Phase 5. The client connection commands below are the intended interface once that phase and Phase 7 ship.

Repository structure

.
├── docs/PLAN.md                    ← SOURCE OF TRUTH (architecture, decisions, phases, E2E bar)
├── README.md                       ← this file (human front door)
├── CLAUDE.md                       ← agent instructions for Claude sessions
├── AGENTS.md                       ← agent instructions, tool-neutral (Codex/Cursor/etc.)
├── .env.example                    ← every env var, documented by name
├── package.json                    ← scripts + pinned deps
├── next.config.ts / tsconfig.json / drizzle.config.ts / vitest.config.ts
│
├── app/                            ← Next.js App Router
│   ├── layout.tsx · page.tsx       ← landing / status dashboard
│   ├── sign-in/page.tsx            ← Google sign-in (resumes interrupted OAuth flows)
│   ├── components/sign-out-button.tsx
│   ├── api/
│   │   ├── auth/[...all]/route.ts           ← better-auth handler (sign-in, /mcp/authorize, /token, DCR /register)
│   │   ├── auth/google-health/start/route.ts    ← health-consent redirect (session-gated)
│   │   ├── auth/google-health/callback/route.ts ← code exchange → encrypt+store → identity map
│   │   └── health/status/route.ts          ← healthcheck (no secrets)
│   └── .well-known/
│       ├── oauth-authorization-server/route.ts
│       └── oauth-protected-resource/route.ts
│   #   app/api/[transport]/route.ts          ← MCP endpoint /api/mcp — ARRIVES in Phase 5
│
├── src/
│   ├── auth/           ← auth.ts (better-auth config), allowlist, app-user resolution,
│   │                     state (health-consent CSRF state), token-service (single-flight
│   │                     refresh), token-store, google-health-oauth, auth-client
│   ├── db/             ← schema.ts (8 domain tables), auth-schema.ts (7 better-auth tables), client.ts
│   ├── security/       ← encryption.ts (AES-256-GCM), redact.ts
│   ├── audit/          ← mutation-audit.ts (insert-only audit writer)
│   └── google-health/  ← registry.ts (data-type single source of truth), scopes.ts, errors.ts
│   #   src/google-health/client.ts + src/time/  ← land in Phase 4
│   #   src/health-services/                       ← shared service layer, Phase 5 (also enables #api)
│
├── drizzle/            ← generated SQL migrations + meta
├── scripts/db-inspect.mjs   ← utility: list/inspect Neon tables
├── tests/unit/         ← Vitest: encryption, redact, allowlist, state, token-service, google-health-oauth
└── .tasks/             ← the task board (see "Task board")

Database tables (15 total): domain — app_users, oauth_connections, oauth_tokens, oauth_states, mutation_audit_log, webhook_events (dormant), data_freshness (dormant), health_cache; better-auth — user, session, account, verification, oauthApplication, oauthAccessToken, oauthConsent.

Setup guide

1. Accounts and services

1. Google Cloud — enable the Google Health API; configure the OAuth consent screen with the googlehealth.* scopes; create an OAuth web client; add the redirect URIs below; publish the app to "In production". Publishing is essential: in Testing status Google expires refresh tokens after 7 days (refresh_token_expires_in: 604799). The "unverified app" badge that appears after publishing is expected and stays — do not submit for verification.

2. Vercel — import this repo as a project. Framework auto-detects as Next.js. Keep Deployment Protection = preview-only (production must stay open so programmatic MCP clients can reach it; the app enforces its own auth).

3. Neon — a Postgres database provisioned via the Vercel Marketplace and connected to the project in the Storage tab. The integration injects DATABASE_URL (pooled) and DATABASE_URL_UNPOOLED automatically.

2. Google OAuth redirect URIs

One web client serves both the better-auth sign-in flow (/api/auth/callback/google) and the Google Health consent flow (/api/auth/google-health/callback). Canonical domain: health.emmetts.dev; the Vercel-assigned google-health-mcp-realemmetts.vercel.app also serves. Register all six:

https://health.emmetts.dev/api/auth/callback/google
https://health.emmetts.dev/api/auth/google-health/callback
https://google-health-mcp-realemmetts.vercel.app/api/auth/callback/google
https://google-health-mcp-realemmetts.vercel.app/api/auth/google-health/callback
http://localhost:3000/api/auth/callback/google
http://localhost:3000/api/auth/google-health/callback

Requested health scopes (nine, minimum-necessary — location/ecg/irn are configured on the consent screen but not requested; there is no settings.writeonly):

Read : googlehealth.activity_and_fitness.readonly
       googlehealth.health_metrics_and_measurements.readonly
       googlehealth.sleep.readonly
       googlehealth.nutrition.readonly
       googlehealth.profile.readonly
       googlehealth.settings.readonly
Write: googlehealth.nutrition.writeonly
       googlehealth.health_metrics_and_measurements.writeonly
       googlehealth.profile.writeonly

3. Environment variables

Every variable is documented by name in .env.example. Values are never committed — locally they live in .env.development.local (gitignored); in production they live in the Vercel env store. Never put secret values in code, logs, the task board, or any markdown.

Generate a key: node -e "console.log(require('crypto').randomBytes(32).toString('base64'))"

4. Local development

npm install
cp .env.example .env.development.local     # then fill in values
npm run dev                                # http://localhost:3000
npm test                                   # Vitest
npm run typecheck                          # tsc --noEmit
npm run db:generate                        # generate a Drizzle migration from schema changes
npm run db:migrate                         # apply migrations (uses DATABASE_URL_UNPOOLED)
node scripts/db-inspect.mjs                # list/inspect Neon tables

Local sign-in needs GOOGLE_CLIENT_ID / GOOGLE_CLIENT_SECRET populated and the localhost:3000 redirect URIs registered (both are in place). The dev box is Windows — all npm scripts must be cross-platform.

5. Deploy

Push to main; Vercel builds and deploys. Migrations are run from a dev machine against the unpooled Neon URL (npm run db:migrate), not in the build. Production env-var changes only take runtime effect on the next deploy. Note: an auto-deploy webhook has occasionally not fired on push — if a deploy doesn't appear, deploy manually via the Vercel CLI.

Connecting an MCP client

Available once the MCP endpoint ships (Phase 5) and prod is wired (Phase 7). Each client walks the OAuth flow and you sign in with the allowlisted Google account.

• Claude Code: claude mcp add --transport http health https://health.emmetts.dev/api/mcp

• claude.ai (web + mobile): Settings → Connectors → Add custom connector → https://health.emmetts.dev/api/mcp → complete OAuth.

• ChatGPT: Add a custom connector — it registers itself via Dynamic Client Registration.

MCP surface

Defined in docs/PLAN.md §"MCP surface (v1)"; input schemas per the handoff spec §11. Every read response carries freshness + units and is payload-bounded (default pageSize ≤ 100; HR series summarized via rollups; truncation notes when capped).

Read tools (9): get_today_steps, get_sleep_summary, get_latest_heart_rate, get_exercise_week, get_nutrition_log, get_health_context (bundle: sleep + latest HR + resting HR/HRV + recent activity + nutrition — data only, no conclusions), query_health_data (generic list/reconcile, registry-allowlisted), rollup_health_data, get_sync_status.

Write tools (5, +1 conditional): create_nutrition_log, update_nutrition_log, delete_nutrition_log, create_hydration_log, update_measurement (weight | body-fat | height). update_profile only if the live v4 REST reference confirms a writable profile endpoint — otherwise dropped.

Resources (5): health://profile, health://settings, health://connected-user, health://data-types, health://freshness.

Absent by design: sleep, exercise, and settings writes; bulk historical writes.

Security posture

• Four auth layers, never conflated (table above). The MCP endpoint requires a valid OAuth token; sign-in is allowlisted to ALLOWED_GOOGLE_EMAILS; DCR is open by design (any client may register — safety comes from the allowlisted login, not registration).

• Google tokens are AES-256-GCM encrypted at rest (TOKEN_ENCRYPTION_KEY, with key_version for rotation). No plaintext tokens in the DB, logs, or error paths — a redact() helper strips token patterns (ya29., 1//, GOCSPX-, JWTs, Bearer/Basic, Neon npg_) before anything is logged.

• Token refresh is single-flight (SELECT … FOR UPDATE on the token row) to avoid concurrent-refresh races; on refresh failure the connection is marked reauth_required.

• Writes (nutrition / hydration / measurements only) are Zod-validated, explicit-input only, and every mutation is audit-logged in mutation_audit_log. There are no sleep / exercise / settings write tools at all.

• No medical diagnosis language anywhere; freshness/limitation notes on every response.

• Production stays open (no Vercel SSO wall) on purpose — the application's own auth is the perimeter.

Troubleshooting

Task board

Work is tracked on a self-contained board under .tasks/ (the SHAUGHV tasks system).

• .tasks/TASKS.md — the board (Backlog / To-Do / Active / Done). Source of truth for what's next.

• .tasks/MILESTONES.md — dated epics; tasks join one with an (ms #id) tag. Current milestone: #v1.

• .tasks/tasks/<id>.md — a rich detail file per task (TT;DR-led, with ## Verification, ## Status, ## Activity). The decision history lives here — e.g. rlw.md (Railway/FastMCP), api.md (REST surface feasibility), inf.md (the infra session), w11.md (webhooks v1.1).

• .tasks/CLAUDE.md — working memory (people, terms, projects, preferences).

The live dashboard is a zero-dependency Node server; resolve its port from .tasks/.board-server.json or run node .tasks/board-server.mjs status. See CLAUDE.md / AGENTS.md for how agents should use the board.

Further reading

• docs/PLAN.md — the authoritative build plan (read first).

• CLAUDE.md — instructions for Claude coding sessions.

• AGENTS.md — the same operational guidance, tool-neutral, for any agent (Codex, Cursor, etc.).

• .env.example — the env-var reference.