# OtoTheory vs Harmony Chack

The clearest difference is update cadence: OtoTheory at every 2 days against Harmony Chack's fortnightly. On price, ads, in-app purchases and device support there is nothing between them.

Both are free to download. OtoTheory sells 2 in-app purchases, starting at $4.99 per month and Harmony Chack sells 1 one-off in-app purchase. Whichever you choose, the download price is not the number that matters.

OtoTheory ships an update every 2 days, Harmony Chack fortnightly. The most recent releases landed on November 5, 2026 and November 6, 2026 respectively.

## The numbers

| Metric | OtoTheory | Harmony Chack |
| --- | --- | --- |
| Price | Free | Free |
| Positive reviews | 90.9% of reviews | — |
| In-app purchases | Yes | Yes |
| Ads | No | No |
| Update frequency | **Every 2 days** | Fortnightly |
| Monetization | Freemium | — |
| Size | 58 MB | 34 MB |
| Requires iOS | 17.0 | **16.0** |
| Devices | iPhone, iPad | iPhone, iPad |
| Age rating | 4+ | 4+ |
| Developer | [NORITO HARADA](https://appshunter.io/developer/1851826664) | [Hironori Karube](https://appshunter.io/developer/1880243912) |

## What reviewers say

### OtoTheory

[App page](https://appshunter.io/ios/app/ototheory-chord-progression/id6755084287)

Create music theory-correct chord progressions intuitively, even without prior knowledge. Features AI song analysis, real-time editing with backing tracks, and MIDI export for digital audio workstations.

**Highlights:** AI Chord Import, Chord Progression Builder, 15 Groove Patterns, 50 Presets, OtoTheory AI Suggestions, MIDI Export, Fretboard & Keyboard Views

**Features:** macOS Compatibility, Vision Pro support

**In-app purchases (2)**

| Purchase | Price | Billing |
| --- | --- | --- |
| OtoTheory | $4.99 | per month |
| OtoTheory Pro (Annual) | $49.99 | per year |


### Harmony Chack

[App page](https://appshunter.io/ios/app/harmony-chack/id6803001408)

**Features:** macOS Compatibility, Vision Pro support

**In-app purchases (1)**

| Purchase | Price | Billing |
| --- | --- | --- |
| プレミアム | $0.99 | one-time |


## Frequently asked questions

### Is OtoTheory free?

OtoTheory is free to download, with in-app purchases available.

### Is Harmony Chack free?

Harmony Chack is free to download, with in-app purchases available.

### Do OtoTheory or Harmony Chack have ads?

Neither OtoTheory nor Harmony Chack shows ads.

### Which is updated more often, OtoTheory or Harmony Chack?

OtoTheory ships an update every 2 days, and Harmony Chack fortnightly. Most recently, OtoTheory was updated on November 5, 2026 and Harmony Chack on November 6, 2026.

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*Compared by [AppsHunter](https://appshunter.io/) from daily US App Store data. Review summaries are generated from verbatim App Store reviews.*