What to Expect in the Snap System Design Interview

The Snap system design interview asks you to design real-time, media-heavy, privacy-focused systems. Mid-level and senior candidates get one dedicated design interview inside the virtual onsite. The questions are based on Snap's own products: disappearing messages, Stories, media delivery, and augmented reality. You are graded on requirements, architecture, trade-offs, and communication.

The Question Types Snap Asks

Snap design questions match problems its engineers solve every day.

• Disappearing messages. Design a chat system where messages delete after they are viewed.
• Stories. Design a feed of posts that stay visible for 24 hours and then expire.
• Media upload and delivery. Design a service that stores and serves millions of photos and videos with low delay.
• Notifications. Design a service that tells millions of users about new messages in near real time.
• Lens delivery. Design a system that sends augmented reality effect files to phones quickly.

What Makes Snap's Problems Different

Four properties separate Snap questions from generic design questions.

Deletion by default. Most systems keep data forever. Snap deletes it. Your storage design needs a TTL, which means time to live: a timer after which data is removed. Interviewers like candidates who treat deletion as a core requirement.

Friend-graph sharing. Snapchat shares content between friends, not to public followers. This keeps fan-out small. Fan-out means the number of receivers one post must reach. Small fan-out changes which parts of the design need caching.

Mobile-first latency. Snapchat opens straight into the camera. Users expect the app to respond within a fraction of a second. Your design should mention CDNs. A CDN is a network of servers that keeps copies of files close to users.

Heavy media traffic. Photos and videos are large. Uploads and downloads are most of the load, so object storage and compression matter. Object storage is a service that stores files by ID rather than in folders.

One Example Question: Design Disappearing Messages

Here is a high-level solution to the most common Snap question.

Step 1: Requirements (about 5 minutes). Users send photo and video messages to friends. A message deletes after the receiver views it, or after 30 days unviewed. Assume 100 million daily users as a working number. Confirm these rules with the interviewer before you draw anything.

Step 2: High-level parts. A mobile client, an API gateway, a message service, media storage, and a notification service. An API gateway is the single entry point that routes requests to backend services.

Step 3: The send path. The client uploads the photo to object storage and receives a media ID. The client then sends a message record holding that ID to the message service. The notification service tells the receiver a message arrived.

Step 4: The delete path. When the receiver views the message, the client reports the view. The message service marks the record and schedules deletion of the media. A background job also deletes anything older than 30 days using the TTL.

Step 5: Trade-offs. Discuss push against pull for notifications. Discuss where encryption happens. Discuss what happens when a delete job fails, and how you retry it safely.

How Interviewers Grade the Round

Interviewers reward a clear order: requirements, estimates, architecture, then depth. They expect numbers, such as storage per day at your assumed scale. They expect at least one trade-off argued in both directions. Silence is the main failure, so explain each choice as you make it. Asking the interviewer questions is graded as a strength, not a weakness. Snap builds products for users first, so tie each technical choice to user experience.

How to Prepare

• Learn the building blocks first. Grokking the System Design Interview explains caching, queues, CDNs, and storage with worked case studies.
• Study reusable patterns. System Design Patterns explains patterns like fan-out and TTL-based cleanup that Snap questions reuse.
• Practice the Snap-specific angle. Redesign one practice answer with deletion by default. Notice how it changes your storage choices.
• See the whole loop. Read What Is the Snap Interview Process Like? (Round by Round) for the rounds around this one.
• Reserve time for values questions. Even design interviews open with behavioral questions at Snap. Prepare with Top Snap Behavioral Interview Questions (and How to Answer Them).