How to play

Draw your system

• Drag parts from Components onto the board.
• Drag from a dot on one box to another box to connect them. Every box has four dots.
• Select a box to change its size or add copies.
• Drag empty space to move around. Pinch, or hold Ctrl and scroll, to zoom.

Press Run and survive

A round passes when all three hold:

• Press Run, or Ctrl+Enter (⌘ Enter on a Mac). The same keys skip to the end of a run.
• A round may have a twist, like a crash or a sale. The first time it is a surprise: read the heads-up, it hints at what may break.
• When a twist hits, you get paged. The page shows what users feel, not the cause. It never changes your result: your design does.
• New parts unlock as you climb.

Fail, learn, fix

• A red circle marks the part that broke, and the coach says why. See what happened has the details.
• Stuck? Use a hint: a nudge first, then the fix. Earn hints by passing rounds and answering quick checks.
• Pass with the cheapest design for three stars. Not there yet? Build it again.

Three ways to play

• Learn: Rounds that each teach one new idea about system design.

• Questions: Popular system design interview questions. Build each design and test it.

• Sandbox: Set your own traffic and twists, and find where your design breaks. No budget, no rounds.