Twitter / X
Real-time social platform with petabyte-scale data and ML ranking systems.
4 Rounds
~14 Days
Hard
The Interview Loop
Recruiter Screen (30 min)
Standard fit check, behavioral questions, and resume overview.
Technical Loop (3-4 Rounds)
Deep dive into domain knowledge, coding, and system design.
Interview Question Bank
Full Stack Engineer
•
Behavioral
•
medium
X operates with a hardcore engineering culture. Tell me about a time you had to ship a critical feature under an extremely tight, almost unreasonable deadline.
#Time Management
#Prioritization
#Resilience
Full Stack Engineer
•
Behavioral
•
hard
Describe a situation where you had to debug a severe production outage. What was your process from discovery to post-mortem?
#Incident Management
#Debugging
#Communication
Full Stack Engineer
•
Behavioral
•
medium
X moves very fast, often requiring decisions without full context. Tell me about a time you had to make a technical decision with incomplete information.
#Decision Making
#Ambiguity
#Risk Management
Full Stack Engineer
•
Behavioral
•
medium
How do you handle disagreements with a senior engineer or product manager regarding the technical direction of a project?
#Conflict Resolution
#Communication
#Teamwork
Full Stack Engineer
•
Behavioral
•
medium
Tell me about a time you identified a major performance bottleneck in your system and took the initiative to fix it without being asked.
#Initiative
#Performance
#Ownership
Full Stack Engineer
•
Behavioral
•
hard
Describe a time you had to take over a legacy codebase with no documentation and the original authors had left. How did you approach it?
#Adaptability
#Problem Solving
#Legacy Code
Full Stack Engineer
•
Behavioral
•
hard
What is the most complex system you have built from scratch, and what were the key technical trade-offs you had to make?
#Architecture
#Trade-offs
#End-to-End Ownership
Full Stack Engineer
•
Coding
•
medium
Write a function to calculate the length of a Tweet. Note that URLs always count as 23 characters, and emojis/special Unicode characters should be counted correctly as single characters despite surrogate pairs.
#String Manipulation
#Regex
#Unicode
Full Stack Engineer
•
Coding
•
medium
Implement a rate limiter for the X API that allows a user to make N requests per time window T. How would you handle this in a distributed environment?
#Sliding Window
#Concurrency
#Distributed Systems
Full Stack Engineer
•
Coding
•
hard
Given K sorted arrays representing timelines of users you follow, merge them into a single sorted timeline of the most recent tweets.
#Heaps
#Merge Sort
#Arrays
Full Stack Engineer
•
Coding
•
medium
Implement an autocomplete system for @mentions. As the user types, return the top 5 matching usernames based on a combination of prefix match and the user's interaction frequency.
#Trie
#Hash Maps
#Sorting
Full Stack Engineer
•
Coding
•
hard
Find the shortest path between two users on X (Degrees of Separation). You are given an API call `getFollowers(userId)`.
#Graph Traversal
#BFS
#Bidirectional BFS
Full Stack Engineer
•
Coding
•
easy
Implement a deep clone function for a complex state object in React, ensuring that nested objects, arrays, and Date objects are copied by value, not reference.
#JavaScript
#Recursion
#Object Manipulation
Full Stack Engineer
•
Coding
•
medium
Design and implement an LRU (Least Recently Used) Cache to store recently fetched tweets on the client side.
#Linked Lists
#Hash Maps
#Caching
Full Stack Engineer
•
Coding
•
easy
Write a function to parse a raw tweet string and extract all valid hashtags, ignoring punctuation immediately following the tag.
#String Parsing
#Regex
Full Stack Engineer
•
Coding
•
medium
Implement a custom debounce function in JavaScript that supports both leading and trailing edge execution. This is used for the search bar on X.
#JavaScript
#Closures
#Asynchronous Programming
Full Stack Engineer
•
Coding
•
medium
Given a stream of tweets, write an algorithm to find the Top K frequent words (Trending Topics) in the last hour.
#Heaps
#Hash Maps
#Stream Processing
Full Stack Engineer
•
System Design
•
hard
Design a real-time Direct Messaging (DM) system for X, supporting 1-on-1 and group chats with read receipts.
#WebSockets
#NoSQL
#Real-time
#Pub/Sub
Full Stack Engineer
•
System Design
•
hard
Design the X Home Timeline. How do you ensure sub-second latency for users with millions of followers?
#Fanout
#Caching
#Message Queues
#Database Sharding
Full Stack Engineer
•
System Design
•
hard
Design X's Trending Topics system. How do you calculate trends in real-time across different geographic regions?
#Stream Processing
#Apache Kafka
#Count-Min Sketch
#Distributed Systems
Full Stack Engineer
•
System Design
•
hard
Design the Like and Retweet counter system. How do you handle the massive write load when a tweet goes viral?
#Eventual Consistency
#Batching
#Distributed Counters
Full Stack Engineer
•
System Design
•
hard
Design a video upload and processing pipeline for X. Users can upload up to 2 hours of 1080p video.
#Blob Storage
#Asynchronous Processing
#CDN
#Video Encoding
Full Stack Engineer
•
System Design
•
medium
Design X's push notification system. How do you ensure notifications are delivered reliably and not duplicated?
#Message Queues
#APNs/FCM
#Idempotency
Full Stack Engineer
•
System Design
•
medium
Design a search system to find specific tweets by a user within a specific date range.
#Elasticsearch
#Inverted Index
#Data Partitioning
Full Stack Engineer
•
System Design
•
hard
Design the architecture for X Spaces (live audio rooms). How do you handle thousands of listeners and multiple speakers with low latency?
#WebRTC
#Audio Streaming
#SFU
#Scalability
Full Stack Engineer
•
System Design
•
hard
Design an ad-serving system for the X feed. How do you select the most relevant ad in under 50ms?
#Machine Learning Inference
#Low Latency
#Auction Algorithms
Full Stack Engineer
•
System Design
•
hard
Design a system to detect and filter out spam or bot replies in real-time before they are rendered to users.
#Machine Learning
#Stream Processing
#Rules Engine
Full Stack Engineer
•
Technical
•
medium
How would you optimize the rendering performance of an infinite scrolling list of tweets in React to prevent DOM bloat and memory leaks?
#React
#Virtualization
#Performance
Full Stack Engineer
•
Technical
•
medium
Explain how you would implement optimistic UI updates for the 'Like' button on a tweet. How do you handle network failures?
#UX
#State Management
#Error Handling
Full Stack Engineer
•
Technical
•
medium
X uses GraphQL heavily. How does GraphQL help in reducing over-fetching in the web app compared to REST, and what are the caching challenges?
#GraphQL
#REST
#Caching
Full Stack Engineer
•
Technical
•
hard
Explain how you would handle state management for a complex web app like X Pro (formerly TweetDeck) with multiple independent columns updating in real-time.
#State Management
#Redux
#React Context
#Architecture
Full Stack Engineer
•
Technical
•
medium
Describe the differences between Server-Sent Events (SSE) and WebSockets. Which would you choose for streaming new tweets to the client and why?
#WebSockets
#SSE
#HTTP
Full Stack Engineer
•
Technical
•
medium
How do you prevent Cross-Site Scripting (XSS) attacks when rendering user-generated content, such as tweets with links and formatting, in the browser?
#XSS
#Security
#Sanitization
Full Stack Engineer
•
Technical
•
hard
What strategies would you use to optimize the initial load time (Time to Interactive / First Contentful Paint) of the X web application?
#Performance
#SSR
#Code Splitting
#Web Vitals
Full Stack Engineer
•
Technical
•
hard
Explain database sharding strategies for storing billions of user relationships (followers/following). What is the shard key?
#Database Sharding
#Scalability
#RDBMS
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