Hacaro vs Keyhole Puzzle
Price, ratings, monetisation and update history for both apps, side by side — with what reviewers say about each.
Hacaro
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– Description The Stroop Test is widely known as a cognitive task related to attention and decision-making, and it is thought to be associated with brain functions such as the frontal lobe and the anterior cingulate cortex. This app provides two types of tasks. In the first task, you are asked to identify the colors red, blue, green, and yellow as accurately and quickly as possible (Color Naming Task). In the second task, even when the meaning of the word and the color of the ink do not match, you are asked to answer based on the ink color, not the word itself (Incongruent Color Naming Task). It is known that responses tend to be slower when the color information and the word meaning are inconsistent compared to when they match. This phenomenon is called the Stroop Effect. This is thought to occur because the processes of recognizing colors and reading words work simultaneously and interfere with each other, which increases the time required for information processing. Each task consists of 20 questions, and after completion, the number of correct answers and the elapsed time will be displayed. The task display language is available in 11 different languages. – Data Sharing Past records can be saved to your device in CSV format or shared with other apps, such as by sending them via email. – Selecting a Mode When Starting the App When launching the app, you can choose from three modes: 1: Hacaro Series Account Mode By logging in with a user account, all past data can be stored securely in the cloud. Even if you change devices, you can access and share your data by logging in with the same account. For more details, please tap “Learn more about the Hacaro Series Account” on the app’s home screen. 2: Guest Mode Up to 30 records are stored locally on the device. Older records will be deleted automatically as new data is added. Even if you log in using another mode later, the 30 guest records will remain stored on the device. 3: Researcher Mode Records are managed using a Subject ID rather than age or gender. At the start of each session, a subject ID selection screen will appear. As with Guest Mode, up to 30 records can be stored.
Keyhole Puzzle
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Keyhole Puzzle is a puzzle where you match the shape displayed on the screen to the “keyhole” shape below. You can play with just one finger. Trace the displayed shape to move it, and align it perfectly with the keyhole to advance to the next puzzle. The gameplay is very simple. Drag the shape displayed above and position it so it fits perfectly into the keyhole below. When the shape matches, you automatically advance to the next puzzle. It's a simple shape-matching puzzle with easy-to-use controls.
Screenshots
Verdict
The clearest difference is update cadence: Keyhole Puzzle at every 2 weeks against Hacaro's every 4 months. On price, ads, in-app purchases and device support there is nothing between them.
Scored on Price · Rating · Positive reviews · Number of ratings · Update frequency · Ads · In-app purchases · Monetization · Best chart rank · Devices · Requires iOS
Both are free to download. Neither carries in-app purchases, so what you see is what you pay.
Hacaro ships an update every 4 months, Keyhole Puzzle every 2 weeks. The most recent releases landed on November 2, 2026 and November 9, 2026 respectively.
| Parameter | Hacaro | Keyhole Puzzle |
|---|---|---|
| Price | Free | Free |
| Update frequency | Every 4 months | Every 2 weeks — better |
| Ads | No | No |
| In-app purchases | No | No |
| Devices | iPhone, iPad, iPod — better | iPhone, iPad |
| Requires iOS | 15.0 — better | 16.0 |
| Further details — not scored | ||
| Size | 117 MB | 1 MB |
| Age rating | 12+ | 4+ |
| Developer | DIGITAL STANDARD CO., LTD. | 順天堂大学 |
In-app purchases
Hacaro
No in-app purchases
Keyhole Puzzle
No in-app purchases








