Best wearable APIs for AI agents: a developer's guide

2026-05-09

If you're building anything that connects health data to AI, your first practical question is which wearable APIs are actually pleasant to integrate against. This piece is from someone who's read all of them.

The criteria that matter:

1. Documented and stable. Public docs, predictable shapes, no quiet breaking changes.
2. OAuth not weird. Standard authorization code flow with refresh tokens, sane scopes.
3. Useful data. Sleep stages, HRV, workouts, daily activity at minimum.
4. Reasonable rate limits. You're not going to be hammering, but you don't want surprise 429s either.
5. Webhook support. So you can react to new data without polling.

Here's how the major ones stack up.

1. WHOOP

Developer portal. HRV in ms_rmssd.

WHOOP's API is the cleanest of the big six. OAuth 2.0 flow is standard, scopes are sensible, the data shapes are well-documented, and you get sleep, recovery, strain, workouts, and HRV in a consistent JSON schema. Rate limits are reasonable; 429s are rare. Webhooks notify you when new data lands.

The downside: subscription-only ($239/year), so anyone you're integrating for has to be a paying WHOOP user. The data depth is excellent if they are.

2. Polar

AccessLink API. HRV in ms_rmssd.

Polar's AccessLink is older and less polished than WHOOP's developer portal, but the underlying API is solid. Sleep stages, training sessions, daily activity, Nightly Recharge, Cardio Load, SleepWise data; depending on the model, you get a lot. Vantage V3 and Pacer Pro expose the full set; entry trackers expose less.

Webhook support is real but the documentation is lean. OAuth is standard. Rate limits are loose.

3. Oura

Cloud API. HRV in ms_rmssd.

Oura's API is well-documented and the v2 endpoints are stable. You get sleep, readiness, activity, heart rate, HRV, and workouts. OAuth is standard. Rate limits are documented and generous for normal use.

The catch is the subscription tier. The hardware is $349 but the API gives you the most when the user is on Oura's app subscription ($70/year). Without it, some daily metrics are degraded.

4. Withings

Developer API. HRV in ms_rmssd.

Withings' API covers a wider range than the others because their hardware does too: scales, sleep mats, blood pressure cuffs, watches. The developer experience is competent, OAuth standard, data shapes consistent.

The minor friction is that Withings auth flows have historically had region-specific quirks (EU vs US OAuth domains). Worth testing in production once before launching anywhere.

5. Garmin

Connect IQ + Health API. HRV in ms_rmssd.

Garmin's developer offering is split across Connect IQ (for on-device apps) and the Health API (for cloud-side data access). The Health API is enterprise-tier in spirit; you go through a developer-program approval process. Once you're in, the data depth is enormous because Garmin makes everything from $200 trackers to $1500 multi-sport watches with chest-strap-class sensors.

OAuth is standard but the approval process gates you. Plan for multi-week onboarding.

6. Suunto

Developer portal. HRV in ms_rmssd.

Suunto's API is multisport-focused: workouts, training metrics, occasional sleep. Less depth than the top four for general health, but if you're building something endurance-specific it's the right fit. OAuth standard, docs reasonable.

Honorable mentions

• Hevy (https://api.hevyapp.com/docs): not a wearable but a strength-training app with a public API. Useful if you're building anything that integrates lifts.
• Intervals.icu (https://intervals.icu/api/v1/docs): aggregator that pulls from Garmin, Strava, etc. Useful if you want endurance analysis as a single feed.
• Dexcom (https://developer.dexcom.com/): CGM, not a wearable in the traditional sense, but their API is the standard for glucose data.
• Apple HealthKit: not a web API, iOS-only. If you're building inside an iOS app it's the right path. If you're building a web service, you can't use it directly.

What about MCP-shaped APIs?

If you're specifically building for AI agents, the MCP-shaped path is to put a server in front of these APIs and expose a single uniform tool surface. That's what Freddy does. It reads from Polar, Oura, WHOOP, Withings, Suunto, Hevy, Intervals.icu, and Dexcom and exposes them to any MCP client. Saves you from writing six OAuth flows yourself.

If you'd rather build the integration yourself, all of the APIs above are fine starting points. WHOOP and Oura are the easiest to get running. Garmin is the most powerful once you're approved.

Verified 2026-05-09. APIs evolve; check the linked developer portals before committing implementation work.