Learn how the apps you love really work.

UPI, WhatsApp, Tatkal and dozens more, explained in plain words. Then build systems yourself in a live simulator.

Start learning, free Try the simulator

Try it: launch day

Turn up the traffic, then add servers until it holds.

Traffic400 requests a second

App servers

1

slowest 1% of requests: –
requests failed: –

Questions from the apps you use every day

Start from a moment you know and work back to the system behind it.

WhatsAppWhat do one tick, two ticks and blue ticks really mean?
Google Pay, PhonePe, Paytm (UPI)Money left your account but never arrived. Where did it go?
IRCTC TatkalHow does Tatkal survive lakhs of people at exactly 10 AM?

See all 62 everyday app lessons

Everything you need to really get it

Stories, not textbooks
Ten-minute lessons that start from a moment you know and explain every word.
A real simulator
Drag in servers and caches, push traffic through, and watch where it breaks.
A plan made for you
One clear next step each day, with reviews just before you'd forget.
Interview practice
A 45-minute mock round with an AI interviewer, graded with clear advice.

Start with one question

Pick an app you use every day and find out what really happens behind the screen.

Start learning, free