HealthLog/docs/integrations/fitbit.md

Fitbit integration (Fitbit & Pixel)

Ended. Google turned the classic Fitbit Web API off on 30 October 2026. HealthLog no longer calls it; existing connections and what they imported stay. Fitbit and Pixel Watch data now come through Google Health.

HealthLog reads Fitbit and Pixel Watch data through the classic Fitbit Web API (api.fitbit.com). The OAuth app is a Fitbit developer app registered at dev.fitbit.com — not a Google Cloud OAuth client. Like WHOOP, credentials are brought per user: each user (or the operator on their behalf) supplies their own Fitbit app's client id/secret in Settings. The internal integration key is fitbit.

Common mistake: the field wants a Fitbit Client ID (a short numeric id from dev.fitbit.com), not a Google Cloud client id ending in .apps.googleusercontent.com. A Google Cloud client fails at the Fitbit consent screen with unauthorized_client — Invalid client_id, because Fitbit and Google Cloud are separate client registries.

The classic Fitbit Web API was turned off on 30 October 2026. Google ended support for it on 30 September 2026 and turned it off on 30 October 2026, after which it "will no longer function or sync data" (Google's migration guide). New app registrations at dev.fitbit.com/apps/new are closed.

Since that day HealthLog no longer calls the Web API for any Fitbit connection: no hourly sync, no backfill, no token refresh, and no new connection. Nothing is deleted. The connection and every reading it imported stay, and the Fitbit card explains the move instead of asking for a reconnect. To keep Fitbit and Pixel data coming, connect the Google Health integration. It reads the same devices, but Google asks for consent once more: Fitbit tokens cannot be carried over.

Where a day imported from Fitbit before the turndown also comes in through Google Health, the source-priority ladder keeps one of them per day (Fitbit ranks just above Google Health by default), so steps, sleep and the other daily values are not counted twice.

1. Use an existing Fitbit developer app

Registration of new apps is no longer possible (see the note above). For an app you registered before the shutdown, these are the settings that matter:

1. OAuth 2.0 Application Type:
   • Personal — the app only ever sees the owner's own Fitbit account, and gets intraday (per-minute) heart-rate/steps automatically. This is the right choice for a single-person self-host.
   • Server (or Client) — needed when the instance connects other people's accounts. Intraday/heart-rate access is then granted case by case via Fitbit's Intraday Data Access request form.
2. Callback URL: https://your-instance.example.com/api/fitbit/callback — absolute, HTTPS, and matching the redirect_uri HealthLog sends (see the redirect-URI note below). One entry per environment you connect from.
3. Scopes: the ones HealthLog requests (next section).
4. The app's settings page shows the Client ID (short, numeric) and the Client Secret — keep the secret out of any chat log.

2. Scopes

HealthLog requests exactly these read scopes (space-separated on the wire):

activity cardio_fitness heartrate oxygen_saturation profile respiratory_rate sleep weight

The temperature scope is intentionally omitted — the classic skin-temperature reading is a baseline delta rather than an absolute value, so it has no honest canonical slot yet. The authorization uses the Authorization Code Grant with PKCE (S256), which Fitbit recommends; HealthLog mints the code_verifier server-side and never exposes it to the browser.

3. Wire the credentials in Settings → Integrations

Credentials are stored per user, not in .env. Sign in as the target user, open Settings → Integrations → Fitbit, and paste the Client ID and Client Secret. They are encrypted AES-256-GCM at rest.

4. Connect

Click Connect with Fitbit. HealthLog redirects to the Fitbit consent screen (www.fitbit.com/oauth2/authorize), exchanges the returned code for an access + refresh token at api.fitbit.com/oauth2/token, stores them encrypted, and runs an initial sync. There is no webhook — Fitbit syncs on the safety-net cron pull. Classic Fitbit refresh tokens rotate (one-time use); HealthLog replaces the stored token on every refresh.

Redirect URI is validated strictly

The resolved redirect_uri is asserted at connect time to be absolute, https (or http on localhost), to target exactly /api/fitbit/callback, and — when FITBIT_REDIRECT_URI is set alongside NEXT_PUBLIC_APP_URL — to share its origin. A misconfigured value fails closed rather than redirecting elsewhere.

Optional instance env var

# Only when the callback origin differs from NEXT_PUBLIC_APP_URL:
FITBIT_REDIRECT_URI="https://your-instance.example.com/api/fitbit/callback"

The Fitbit client id/secret are per-user (Settings), not env vars.

Source overlap

If Fitbit and another source (Withings, WHOOP, Apple Health) both supply the same vital — resting heart rate, blood oxygen, body temperature or respiratory rate — the source priority ladder in Settings → Source priority decides which one wins per metric. FITBIT is ranked in every default metric ladder; override per metric on that page.

Disconnect

The Settings Disconnect button revokes the stored tokens and removes the connection. Previously synced measurements stay in the database.