Mock system design interview at Dropbox

A live 45-minute round on a question reported in Dropbox interviews, run by an AI interviewer that asks one thing at a time, probes what you say, looks at your whiteboard, and weighs what that round is reported to weigh. It ends with a debrief: a score, what was strong, what was missing.

your question

Design Google Docs

Real-time collaborative editing: many cursors in one document, every keystroke converging to the same text, offline edits merged on reconnect.

You will not see the requirements, the numbers or the design before you start. That is the point.

Walk through it first

What the Dropbox round is reported to look like

60 minutes, practical and product-shaped: a Dropbox product or one part of it, such as file sync, storage, sharing or an API for working with files at scale.

What it weighs

File content kept apart from its metadata, at very large scale
An API that covers the whole life of a file, not only the upload
Fault tolerance: what breaks first, and what happens then
Tradeoffs said out loud at each decision

The common mistake

Going deep too early, or adding parts without a reason. Interviewers are reported to want a practical high-level design first, with detail where they steer, and a queue or cache with no stated purpose counts against you.

From public interview guides and candidate reports, and Dropbox’s own interview guidance where it publishes any. Not endorsed by Dropbox. The interviewer is an AI running in that style; it is practice, not a prediction.

Start the round

Timed · 45 minutesInterview conditions. The AI interviewer owns the clock; the AI Mentor is off.With the AI Mentor · untimedNo clock, and an AI Mentor beside you to ask when you are stuck.

The interviewer’s opening question is free. Answering it is part of Pro. See an example round and its debrief →

The 5 questions this round draws from

Each is reported in Dropbox interviews. Pick one to sit, or read its reference design and walk through a strong answer first.

Design Google DocsReal-time collaborative editing: many cursors in one document, every keystroke converging to the same text, offline edits merged on reconnect.
drawn
Design DropboxKeep a folder identical on every device: upload huge files in resumable chunks, push only what changed, and reconcile two machines that both edited the same file offline.
Design GmailReceive, filter, store and search email for 1.5 billion users: 200 billion inbound messages a day, mostly spam, kept for 20 years.
Design an Object Storage ServiceAn S3-like store for objects from bytes to terabytes, with eleven nines of durability and strong read-after-write consistency at exabyte scale.
Design PastebinStore and serve 10 M text pastes a day behind unguessable links: expiry that is never late, burn after reading, and abuse takedown.

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