System Design Arcade — by Hyperfocused Engineer
Effective date: August 18, 2026
Previous versions: August 9, 2026; February 28, 2026
System Design Arcade is a mobile app that teaches system design concepts through interactive, arcade-style games. This policy explains what data we collect, why, and how we handle it.
The short version: We collect your email and game progress if you sign in, and we measure how the app is used so we can improve it. We don't sell your data, we don't run ads, and we don't build advertising profiles.
If you play as a Guest:
If you sign in (Google, GitHub, Apple, or email):
We do not collect your location (beyond the country code above), contacts, photos, microphone input, browsing history, or advertising identifiers.
We use PostHog for product analytics, so we can see which parts of the app work and which don't. This applies to both Guest and signed-in users.
What we measure:
If you are signed in, these events are linked to your account and email. If you are a Guest, they are linked only to a random device identifier.
We do not use session recording, screen recording, or heatmaps — these are switched off. We do not use analytics for advertising, and we do not share or sell this data.
Analytics events are retained for 12 months. There is currently no in-app switch to turn usage analytics off — email us if you would like your analytics data deleted.
When the app hits an error, a diagnostic report is sent to PostHog so we can fix it. A report contains the error type (for example TypeError), the error message, and a stack trace showing where in our code it happened. It also carries the same app version, device and session information as our other analytics events, and — if you are signed in — is associated with your account.
Error messages can occasionally contain incidental data such as an account identifier or a file path. We make a best effort to keep personal data out of these reports and are actively improving how they are filtered before they leave your device.
We do not collect crash reports from the operating system itself.
Some architecture challenges offer optional AI feedback. This is switched off unless you turn it on, and limited to a few uses per day.
If you enable it, the following is sent to our AI coaching service — a Cloudflare Worker we operate, which passes the request to Groq (running Meta's Llama models) — each time you ask for feedback:
What is kept: our Worker does not log request contents and stores nothing. Groq states that it does not train models on API data and does not retain it by default; it may keep temporary logs for up to 30 days when investigating errors or abuse. See the Groq data policy.
Nothing is sent to this service unless you have switched the AI coach on. You can turn it off again at any time in Settings.
System Design Arcade has public leaderboards. If you are signed in and appear on one, the following is publicly visible — including to people who are not signed in:
Your email address is never shown on a leaderboard.
You can remove yourself from public leaderboards at any time: Settings → Privacy → "Show me on leaderboard". You will still appear on the friends leaderboard of people who have added you as a friend. Guests do not appear on any leaderboard.
If you turn on study reminders, the app schedules notifications locally on your device. We do not use a push notification service and we do not collect a push token.
We do not sell your data, share it with data brokers, use it for advertising, or use it to build profiles for any purpose other than improving this app.
We use the following third-party services:
We do not use any advertising networks, ad SDKs, or advertising identifiers.
Account data is retained as long as your account exists.
If you delete your account, your profile, game progress, statistics and event registrations are permanently deleted from our database, and your login is removed. Two things deliberately survive:
Analytics events are retained for 12 months from when they were recorded. The user profile PostHog builds from them persists until you ask us to remove it.
You can:
The data controller is Hyperfocused Engineer, contactable at the address below.
Where the GDPR or UK GDPR applies, we rely on: performance of a contract for authentication and progress sync; legitimate interests for usage analytics and error diagnostics, so we can keep the app working and improve it; and your consent for the optional AI Design Coach, which you can withdraw at any time by switching it off.
Supabase, PostHog, Groq and our AI coaching service are hosted in the United States. Transfers out of the EEA and UK rely on the European Commission's Standard Contractual Clauses.
In addition to the controls listed above, you may request access to the personal data we hold about you, a portable copy of it, correction of anything inaccurate, restriction of processing, or object to processing based on legitimate interests. Email us and we will respond within 30 days. You also have the right to complain to your local data protection authority.
For California residents: we do not sell or share your personal information as those terms are defined by the CCPA, and we have not done so in the preceding twelve months. The categories we collect are identifiers (email, account and device identifiers, IP address), internet activity (how you use the app), and approximate location limited to a country code.
System Design Arcade is not directed at children under 13. We do not knowingly collect personal information from children under 13. If you believe a child has provided us with personal data, please contact us and we will delete it.
We may update this policy from time to time. Changes will be posted on this page with an updated effective date. Continued use of the app after changes constitutes acceptance of the updated policy.
Questions or requests? Reach us at:
hyperfocusedengineer@gmail.com