# Nodly: Sleep Debt & Caffeine — Circadian Rhythm & HRV Tracker

> Circadian Rhythm & HRV Tracker (iPhone/iPad app by Eiji Shibayama.)

- Source: https://appshunter.io/ios/app/nodly-sleep-debt-and-caffeine/id6801812605 (this page in markdown: same URL + `.md`)
- Developer: [Eiji Shibayama](https://appshunter.io/developer/6790104567)
- Category: Health & Fitness, Lifestyle
- Price: Free with in-app purchases
- Age rating: 12+
- Requires: iOS 17.0 · 8 MB
- Languages: American English, Japanese
- Released: 2026-10-05
- Data updated: 2026-10-09

## What is Nodly?

Sleep debt does not disappear in a single night.
Nodly visualizes accumulated sleep debt, estimates daily cognitive readiness, tracks active caffeine clearance, and guides evening bedtime relaxation—all in one place.

Powered exclusively by on-device processing from Apple Health data, Nodly helps you understand how much energy you have today, when to stop drinking coffee, and when to start winding down for sleep.

[Key Features]

1. Sleep Debt & Daily Readiness
- Estimates sleep debt in hours using a 14-day exponential decay weighted model.
- Combines sleep duration, Heart Rate Variability (HRV), and resting heart rate against your 7-day baseline to display a 0–100 Readiness score.
- Clearly flags "Preliminary" or "Not Measured" when data is insufficient.

2. Caffeine Clearance & Cutoff
- 1-tap logging for coffee, tea, espresso, and energy drinks.
- Calculates active blood caffeine (mg) using personal half-life exponential clearance.
- Dynamically estimates your personalized evening caffeine cutoff time.
- Syncs directly with Apple Health.

3. 24-Hour Circadian Timeline
- Visualizes daily biological milestones: morning sunlight window, peak focus hours, caffeine cutoff, optimal bath timing, and recommended bedtime.
- Weekly Bedtime Goals: set the bedtime and wake time you are aiming for on each weekday, and Nodly uses it as the basis for tonight's guide.

4. Apple Watch Haptic Sleep Guide
- Silent, soothing wrist vibrations guide bedtime relaxation breathing without disturbing your partner.
- 4-7-8 Sleep Breath (Inhale 4s, Hold 7s, Exhale 8s)
- Box Breathing (Equal 4-4-4-4 rhythm)
- 4-6 Calming Breath (Extended exhale)
- View readiness, sleep debt, and log caffeine directly from your wrist.

5. Widgets & Live Activities
- Lock Screen and Home Screen widgets for instant glanceability.
- Interactive Home Screen widget with 1-tap caffeine logging.
- Real-time caffeine tracking in Live Activities and Dynamic Island.

[Zero-Knowledge Privacy]
- No accounts, no sign-ins, zero external servers.
- All biological calculations run 100% on your device.
- Your daily morning check-in is saved to Apple Health so it stays with your Health data.
- On-device CSV export for your sleep and caffeine records.

[Nodly Pro Features]
- Sleep Schedule Shift Plan: Stepwise circadian realignment over 3–14 days.
- Today's Rhythm widget: today's circadian events and your next action on the Home Screen and Lock Screen.
- 24-Hour Estimated Alertness Rhythm curve.
- Caffeine sleep impact tendency analysis, with personal half-life auto-calibration.
- Social Jetlag analysis & guidance.
- Sleep Color Noises (Brown, Pink, Green, White, and Blue noise plus a 432Hz tone).

[Terms & Privacy]
- Terms of Use: https://eira-labs.com/terms.html#nodly
- Privacy Policy: https://eira-labs.com/privacy.html#nodly

[Medical Disclaimer]
Nodly is a wellness tool designed for lifestyle and self-care tracking, not a medical device. All scores, sleep debt estimates, and recommendations are general guidelines and do not substitute professional medical advice, diagnosis, or treatment.

## Pricing and in-app purchases

Base price: Free.

**Subscriptions**

| Subscription | Price | Period |
| --- | --- | --- |
| 月額プラン | $2.99 | per month |
| 年額プラン | $22.99 | per year |

**One-time purchases**

| Purchase | Price | Type |
| --- | --- | --- |
| 買い切り（Lifetime） | $59.99 | one-time |


## Is Nodly safe?

Not enough ratings yet to assess Nodly.

## Is Nodly legit?

Nodly: Sleep Debt & Caffeine appears legitimate, with a few gaps. The AppsHunter Legitimacy Score for Nodly is 65 out of 100 points across 7 verification signals from App Store and developer data.


## Version history (last 1 release)

### 1.0.0 — 2026-10-05

No release notes.

## Apps similar to Nodly

| App | Rating | Price | Category |
| --- | --- | --- | --- |
| [Sleep Debt Tracker & Coach](https://appshunter.io/ios/app/sleep-debt-tracker-and-coach/id6816373249) | — | Free | Health & Fitness |
| [Somnara: Sleep Debt Tracker](https://appshunter.io/ios/app/somnara-sleep-debt-tracker/id6747092614) | — | Free | Health & Fitness |
| [DotSleep - Sleep Debt Log](https://appshunter.io/ios/app/dotsleep-sleep-debt-log/id6764863862) | — | Free | Health & Fitness |
| [Sleep Debt: Rest & Recover](https://appshunter.io/ios/app/sleep-debt-rest-and-recover/id6772904733) | — | Free | Health & Fitness |
| [Sleeply: Sleep Debt & Planner](https://appshunter.io/ios/app/sleeply-sleep-debt-and-planner/id6761580079) | 5.0 (1) | Free | Health & Fitness |
| [Circadian: Sleep & Energy](https://appshunter.io/ios/app/circadian-sleep-and-energy/id6759719638) | 5.0 (4) | Free | Health & Fitness |

## More apps by Eiji Shibayama

- [麻雀ヘルパー - AIカメラ手牌スキャン＆点数計算](https://appshunter.io/ios/app/ai/id6794306978)
- [Carnival - NAS動画・音楽プレーヤー](https://appshunter.io/ios/app/carnival-nas/id6815229809)

All apps by Eiji Shibayama: https://appshunter.io/developer/6790104567

## Related topics

[nodly](https://appshunter.io/ios/topics/nodly) · [caffeine tracker & sleep clock](https://appshunter.io/ios/topics/caffeine-tracker-sleep-clock)

---

*Data collected daily from the US App Store and indexed by [AppsHunter](https://appshunter.io/). User reviews are verbatim App Store reviews. Ratings, prices and chart positions refresh continuously; this snapshot is from 2026-10-09.*