Questions, answered.

A place to learn system design one decision at a time. Each design is split into short topics that follow an interview: requirements, estimates, the API, the data model, the high-level design, deep dives and trade-offs. Diagrams you can step through and quick checks along the way show whether an idea has landed.

Engineers preparing for system design interviews, and anyone who wants to understand how the products they use every day could be built. You can start from the fundamentals or jump straight to a full design.

Today: Agentic, Backend, Frontend and Machine learning. On the way: Generative AI, Application architecture, Data engineering and Database design. Each stack pairs its core concepts with full designs of real-world products.

No. Every design is illustrative: one sound way to build a product like it, explained with its trade-offs. Arrowbox isn’t affiliated with the companies whose products we use as examples.

Start with the roadmap for your stack. It sets out what to learn in what order, which designs to practise on, and how to spend the time in the interview itself.

You can browse the stacks and systems without one. Topics are for signed-in readers, so sign up (it’s free) to read them and keep your place.

As you read, Arrowbox notes the sections you finish and how you do on the quick checks. Your progress shows on each stack’s board and follows your account across devices.

Sign in and you can read 2 designs in full: Phone number and OTP login (Instagram) and News feed (Facebook). In every other design you get its introduction and opening section, so you can see how it starts before you upgrade.

In India, ₹2,830 a month or ₹10,190 a year. Everywhere else, $20 a month or $72 a year. Paying yearly costs about a third less than twelve monthly payments.

In India by card or UPI, elsewhere by card. The currency follows your billing country, not where you browse from. Payments are handled by Razorpay, so your card details never reach us.

Yes, they’re on the way. The Interview plan and its price will be announced when they launch.

Yes. Pro renews at the end of each month or year until you cancel. If a renewal payment doesn’t go through, Pro stays on for a few days while the payment is retried.

From your account page, choose Cancel subscription. It won’t renew and you won’t be charged again; Pro stays on until the end of the period you’ve already paid for.

If a payment is taken twice for the same thing, for example a second subscription started by accident, the extra payment is refunded automatically.

We update the designs regularly and keep adding new ones: new topics, new systems and whole new stacks. Every topic shows the date it was last updated, so you can see how current it is.

Topics are checked for facts and originality before they’re published, and those that have passed a full review carry a Reviewed badge. Where a design relies on public material, its sources are listed.

Use Report an issue at the end of any section. You can also tell us whether a section was helpful; both go straight to the people who write the content.

Choose I want to read this on any topic that isn’t written yet. It moves the topic up our writing list.

Yes. Choose Continue with Google on the sign-in page. If you already have an account with the same email, Google signs you in to it, and your password keeps working too.

From your account page. We send a link to the new address to confirm it, and let your current address know.

Yes. Download my data, on your account page, gives you your profile, reading progress and the feedback you’ve sent as a JSON file.

From your account page. Your account, progress and feedback are deleted for good and you’re signed out everywhere. A subscription is cancelled first, so you’re never charged again.