System Design Interview Prep

The AI does the coding.
You do the thinking.

Comebck is an AI-powered platform where you practice system design interviews by architecting real systems. An AI assistant writes code, an AI judge evaluates your decisions, and a live visualizer renders your architecture.

Everything you need to ace system design

A complete IDE experience with AI assistance, live visualization, and automated evaluation — all in your browser.

AI Coding Assistant

An integrated Gemini-powered assistant that writes code on your behalf. You direct the architecture; the AI handles implementation.

AI Judge

Automated evaluation engine that scores your system design decisions across 7 criteria: scalability, reliability, caching, consistency, security, code quality, and AI utilization.

Architecture Visualizer

Real-time graph rendering of your system design. See API endpoints, databases, caches, and queues as interactive nodes that update as you code.

Live Code Execution

Compile and test your Python implementations in the browser. Run against predefined test suites that verify HTTP endpoints, input validation, and security.

Real-world case studies

Problems modeled after actual systems at Google, Apple, and Microsoft. Not abstract textbook exercises.

Free

Google

Scalable URL Shortener
Design a URL shortening service handling 100M redirections/day with caching, analytics, and rate limiting.
Caching
Base62 Encoding
Rate Limiting
CAP Theorem
Pro

Apple

Notification Delivery Service
Build a push notification system with priority queuing, offline delivery, and device management.
Message Queues
Pub/Sub
Store-and-Forward
TTL
Pro

Microsoft

Distributed Key-Value Store
Implement a distributed KV store with consistent hashing, tunable consistency, and fault tolerance.
Consistent Hashing
Vector Clocks
Replication
CAP Theorem

Simple pricing

Start free. Upgrade when you're ready.

Free
Get started with one case study

$0

1 case study (Google URL Shortener)
AI Assistant (20 interactions/session)
Architecture Visualizer
AI Flashcards
Basic AI Judge report (score only)
Start Free
Recommended
Pro
Full access to all features

$29/month

All 3 case studies (Google, Apple, Microsoft)
Unlimited AI Assistant interactions
Full AI Judge reports with feedback
Submission history & progress tracking
Priority execution
PDF evaluation reports
Start Pro Trial