Privacy policy

Last updated 21 October 2026

This page explains, in plain language, what System Design Visualized ("we") stores when you use the site, why, and what you can do about it. We collect as little as we need to run the course.

Without an account

You can use the lessons, animations, code challenges, quizzes and flashcards without signing up. Your progress is then kept only in your browser's local storage, on your device. We don't receive it.

With an account

When you create an account we store:

• Your name, email address and time zone. To log you in, show your name and count daily streaks in your local time. If you sign in with Google, we receive your name, your email address and a Google account ID from Google, and nothing else.
• Your password, as a one-way hash (scrypt). We never store or see the password itself. Accounts created with Google have no password.
• Your learning activity: lessons completed and time spent on them, quiz answers, review schedule, bookmarks, interview-simulator designs, their evaluations and your answers to follow-up questions. This is what powers your dashboard, spaced review and recommendations.
• Your goals and settings: your weekly goal, your interview date if you set one, and whether you want reminder emails and appear on the leaderboard.
• Your certificate, if you earn one: your name and the date, on a public page anyone with the link can open (that's how certificates are verified).
• A session record (a hashed session token, its expiry and your browser's user-agent string) so you stay logged in.
• A daily count of coach messages, to apply a fair-use limit. The messages themselves are not stored.
• A log of reminder emails sent to you, so you never get the same one twice.

Leaderboard

The weekly leaderboard is off unless you turn it on. If you join, other learners see your first name, the initial of your last name and the XP you earned that week. You can leave it at any time in Settings.

Emails

Besides password resets you ask for, we may send a welcome email after you sign up, a reminder in the evening when a streak of two or more days is about to end, and a reminder when review questions have piled up while you were away. Never more than one reminder a day. Every reminder has a one-click unsubscribe link, and you can switch them off in Settings.

Visit statistics and error reports

To learn which pages help people and where the site breaks, we count page views and button clicks without cookies and without storing your IP address. Each visit is identified only by a code made from your IP address, browser and a secret that changes every day, so we can count visitors per day but cannot recognise you on another day or follow you across sites. We also keep the website that linked you here (just its name, like "google.com"). Statistics are skipped entirely if your browser sends a "Do Not Track" or "Global Privacy Control" signal. Raw statistics are deleted after 13 months.

If the site hits an error in your browser, it sends us the error message, a technical stack trace and the page you were on, so we can fix it. It doesn't include anything you typed.

Cookies and local storage

We use one cookie, sdv_session, which keeps you logged in, plus a short-lived sdv_oauth cookie for the few minutes a Google sign-in takes. Both are HttpOnly, so scripts can't read them. We don't use advertising or tracking cookies. Your browser's local storage keeps preferences such as the theme, your flashcard schedule and, if you are not logged in, your progress. If you install the app, your browser also keeps a copy of the site's files so lessons open offline.

Services we rely on

• Google Fonts serves the site's typefaces, so your browser requests them from Google.
• Google Sign-In, only if you choose "Continue with Google".
• An AI model provider, when the AI coach is switched on. Messages you send to the coach, and the design you submit for an AI review, are sent to that provider to generate a reply. Don't include personal information in them.
• An email provider, to deliver password-reset links and the emails described above.
• Razorpay, if you buy Pro. You pay in Razorpay's secure window; your card, UPI or bank details go to Razorpay, never to us. We keep only the order and payment reference, the plan and the amount, as a record of your purchase.

We don't sell your data or share it with anyone else.

Your choices

• Export: download everything stored about your account from Settings.
• Delete: delete your account from Settings. This permanently removes your account and all of the data listed above, including your certificate page.
• Correct: change your name, time zone, goals and email and leaderboard choices in Settings at any time.

Security

Passwords are hashed, session tokens are stored only as hashes, the site sends strict security headers, and every request for your data is checked against your session. No system is perfectly secure, but we take reasonable care to protect what you trust us with.

Changes

If this policy changes in a way that matters, we'll update this page and the date at the top before the change takes effect.

Questions about your data? Email .