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Interview prep · iOS and Android

Mobile system design interview: how Meta, Google, Uber and others test it

The mobile system design interview is the round where an iOS or Android engineer designs an app or a client library out loud. Most guides teach a framework for answering it. This one is about how companies actually run it: who asks it and at which level, the prompts candidates report, the follow-ups, and what got people turned down. The constraints are the test, and the interviewer expects you to raise them.

Updated 12 October 2026 · from candidate reports dated 2016 to 2026 and company pages

The short version

  • Meta, Google, Uber, DoorDash and Lyft run a mobile design round for iOS and Android engineers, mostly from mid-level up.
  • The prompts candidates report most are a client SDK or library, and a chat app with images.
  • Some mobile candidates still get a backend design question. Ask your recruiter which one you have.
  • The follow-ups keep raising the difficulty: pagination, offline edits, sync, a bad network.
  • Candidates fail by starting with servers, staying too simple, or waiting to be asked about offline and caching.

Is your round mobile or backend?

This is the question candidates ask most, and the honest answer is that it depends on the interviewer. One candidate wrote that “some interviewers are focused completely on frontend side, some want you to shine on FE + BE both”. Another found that starting with the backend got them pulled back to the app, and starting with the app got them pulled to the backend. Candidates at Meta (2017), Google (2022) and Amazon (2025) were given a design question with no mobile angle at all, and one Android engineer put it down to the interviewer not being a mobile developer.

Recruiters do not always know either. One candidate's written guide described a generic system design round, and the recruiter, asked directly, confirmed it would be mobile. So ask, then prepare for both: the app in depth, and enough of the backend (the API, sockets, pagination) to talk about it. A Meta E5 iOS candidate in 2024 said their round was mostly iOS, “You should definitely know some backend stuff tho”.

Which companies run a mobile system design round

Counts are independent candidate reports found in one pass of Reddit and LeetCode Discuss, with Glassdoor and Blind read as search snippets only. Treat the counts as how well documented each round is.

Meta

Mobile design round, 45 minutes, usually no code. Meta's own Android prep page asks how you would design an email client

One round at E4 and E5, two at E6 · About 12 reports, plus Meta's own page

Google

An Android or iOS domain round. L5 Android candidates were offered three algorithm rounds and one Android round, or two and two

Design from L5; L4 reports conflict · About 9 reports

Uber

A mobile systems design round, often a client SDK. One report calls it the Design and Bar Raiser round

Mid-level and up · About 7 reports

DoorDash

An architectural interview where you are given a feature and whiteboard an iOS system, in the words of its iOS team

L4 and up, per DoorDash · DoorDash's blog and 3 reviews

Lyft

An architecture round of about an hour without coding, in Glassdoor reviews from 2017 and 2020; one asked for the server API first, then the client

Mid-level and up · 4 reports

TikTok

Two 30-minute design rounds in one 2024 iOS loop: a past project, then design WhatsApp

One report, iOS 2-2 · 1 report

Agoda

A mobile system design round alongside a separate Android platform round

One report, staff · 1 report

Amazon

A 2022 recruiter promised a mobile design round; 2025 Android candidates found it generic, or were told to skip it at SDE I

SDE II and up · 3 reports

We found no mobile design reports for Airbnb, Snap, Pinterest or Robinhood. Shopify's published process has no system design stage at all; read the Shopify guide for what it runs instead.

The prompts candidates report

Grouped by the kind of problem, with the number of independent reports:

A client library or SDK 6 reports

A feature flag SDK, a places search SDK with a search bar (Uber); an in-house push notification system (Meta); a disk cache for several platforms (Spotify, 2020); an image caching library

Chat or messaging, usually with images 4 reports

A 1:1 chat for sharing images and text (Meta); a chat app (Uber); design WhatsApp with group chat and stickers (TikTok)

A feed, stories or photo app 3 reports

Something like Instagram stories (Meta, 2022); a photo sharing app (Meta); an API for an app holding a user's photos, asked on several occasions

Google's own one-offs 1 report each

An app controlling a Google neon logo on a bad network; a collaborative task list; a YouTube-like app, then a bug that only happens at certain times of day; a stopwatch

Library questions deserve more practice than most prep lists give them: at Uber they were the most common prompt in our sample. Design an app like Uber with live driver location, a standalone offline-first notes app, a news feed, a video player and a file downloader all appear on prep lists, and we found no candidate who was asked them. They can still come up. Prepare the patterns underneath them.

What interviewers probe

The opening prompt is the easy part. Candidates describe follow-ups that keep raising the difficulty, and these are the ones they name:

Why candidates fail it

The round can decide the outcome on its own. An Uber SDE 2 Android candidate in 2024 was turned down because of the design round after positive feedback on both coding rounds, and an Uber L4 Android candidate in 2025 got a no hire on the design round although it felt like it went well.

How to prepare

  1. Ask your recruiter whether the design round is mobile or general, and who usually runs it.
  2. Practise one client library end to end, such as an image cache or a feature flag SDK: its public API, threading, memory and disk limits, and how an app adopts it.
  3. Practise one chat app with images: the API, local storage, sending while offline, and delivery and read states.
  4. For every design, say what lives on the device and what lives on the server, and why, before the interviewer asks.
  5. Draw what happens when the network drops in the middle of a write, and when two devices change the same thing.
  6. Rehearse the follow-ups candidates report: pagination with new items, cache versus always fetch, REST against the alternatives.
  7. Prepare one real story about a performance or reliability problem you fixed in an app, with the numbers.
  8. Give a reason for every choice as you make it: the library, the storage, the sync strategy.

Role-level detail on the iOS and Android loops is in the senior iOS engineer and senior Android engineer guides, and the general version of the round is covered in the Google system design section.

Questions

What is a mobile system design interview?

A round of about 45 to 60 minutes where an iOS or Android engineer designs an app or a client library out loud, usually with little or no code: the screens' data, the API to the backend, caching, offline behaviour and sync. Meta, Google, Uber, DoorDash and Lyft all run a version of it for mobile engineers.

Is the mobile system design round different from backend system design?

It is meant to be, but candidates at Meta, Google and Amazon have been given a backend design question in a mobile loop, and one engineer put it down to an interviewer who was not a mobile developer. Ask your recruiter which kind of design round you have, and prepare enough backend (sockets, pagination, the API) to hold a conversation either way.

What questions are asked in mobile system design interviews?

The prompts candidates report most are a client library or SDK, such as a feature flag SDK, an image or disk cache, a places search SDK or a push notification system, and a chat or messaging app, usually with images. A feed, stories or photo app comes next. Prompts like design Uber with live driver location show up on prep lists far more than in candidate reports.

Which levels get a mobile system design round?

Mostly mid-level and above. Meta runs one design round at E4 and E5 and two at E6. Google Android candidates report design from L5. DoorDash says its system design interview is typically for L4 and up, and 2025 Amazon SDE I reports had it skipped or generic.

Why do people fail the mobile system design interview?

The reasons candidates report: starting with backend servers when the interviewer wanted the app, a design called too simplistic, waiting for the interviewer to raise offline mode and caching, and choosing a tool because it is popular. At Uber, one candidate was turned down on the design round despite positive feedback on both coding rounds.

Your mobile role

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Sources

Mobile System Design Interview: Prompts by Company — Calibrd