Incident LabJoin the waitlist
Private beta · join the waitlist

Learn system design by fixing outages, not memorising diagrams.

Every lab hands you a running React → Node → Postgres app and then breaks it: viral traffic, a dead primary, a botnet, a hot key. You fix it on a canvas with real building blocks, and a simulator grades your design against hidden test cases.

One email per person. No spam - just your invite when we launch.
137
labs, on-calls & capstones
54
interview problems
8
scored mock interviews
Day 4 · LabLIVE SIM
Run 1 · normal day · 900 req/s
UsersReact apptraffic sourceLBLoad balancerL70% busyAPIAPI · Node.js6 × medium0% busySQLPostgreSQLprimary · small0% busyRDSRedis cache2 × 32 GB
traffic
–
p99
–
errors
–
cache hits
—
✓ Normal redirects · p99 ≤ 100 ms✗ Viral link spike · errors ≤ 0.5%✗ Hidden: cache restart (cold)

Not a video. The same simulator that grades the labs is running in this tab.

The roadmap

From your first request to a multi-region payment system

  1. DAYS 1-5

    Foundations

    • System design basics
    • Networking
    • Databases
    • Caching
    • Architecture
  2. DAYS 6-10

    Scaling core

    • Load & scaling
    • DB scaling
    • Replication
    • Advanced caching
    • Messaging
  3. DAYS 11-13

    Production readiness

    • Reliability
    • API design
    • Storage & CDN
  4. DAYS 14-15

    Case studies

    • WhatsApp
    • Twitter timeline
  5. DAYS 16-24

    Advanced

    • Locks & consensus
    • Sagas & outbox
    • Multi-region
    • Observability
    • Security
    • Performance
    • Dropbox
    • Uber
    • Payments
  6. DAYS 25-30

    Interview mode

    • Mock interviews
    • Estimation
    • Communication
    • Final simulation
Everything in one place

One platform from first principles to the offer

30-day path

132 lessons, a lab every day, checkpoints unlock phases.

Problem bank

54 classics graded by hidden tests.

Mock interviews

Timed and scored against your level.

Concept library

Search any idea, jump to the lesson.

Cheat sheet

Numbers and formulas on one page.

Spaced repetition

Flashcards right before you forget.

Study plans & tracks

Meta, Google, Amazon, or a 2-week crash.

How every lab works

Break → diagnose → fix → get graded

  1. 01

    Something breaks

    You get paged, just like on call.

  2. 02

    Find the bottleneck

    Nodes turn red. Graphs show where.

  3. 03

    Change the design

    Drag in real building blocks.

  4. 04

    Pass hidden tests

    Graded by simulation, within budget.

What you will master

Every area a senior system design interview probes

01

Fundamentals

Requirementslatency vs throughputpercentilesavailability
02

Networking

HTTPTLSDNSload balancers
03

Data storage

SQL vs NoSQLACIDindexesstorage engines
04

Caching

Cache-asidewrite policiesevictioninvalidation
05

Scaling

Stateless serviceshorizontal scalingLB algorithmsautoscaling
06

Partitioning

Shardingshard keyshot partitionsconsistent hashing
07

Replication & consistency

ReplicasquorumsCAPread-your-writes
08

Async & messaging

Queuespub/subKafkastream processing
09

Reliability

Rate limitstimeoutsretriescircuit breakers
10

Distributed systems

Locksleader electionRaft/Paxossagas
11

Operations & security

ObservabilitySLOsauthgateway
12

Algorithms & estimation

Bloom filtersHyperLogLoggeo-indexescapacity math
Interview mode

Practise the 45 minutes, not just the answers

A timer, a design the simulator grades, then follow-ups. Scored against the E4, E5 or E6 bar.

  • Twists mid-design: traffic ×10, region outage, budget cut
  • Estimation gym with worked answers
  • Staged capstones: WhatsApp, Twitter, Dropbox, Uber, Payments
Mock interview · Top-K trending · target E5⏱ 23:41
Problem navigation78
Solution design92
Technical excellence64
Communication81
Lean no hire at E5 · drive two deep dives: hot keys and window state
Problem bank

The classics, graded by simulation

Design a URL shortener

easy
hashingcache-asideread-heavy

Design a news feed

medium
fan-outtimeline cachehot keys

Design a chat app

medium
WebSocketsorderingoffline delivery

Design Top-K trending

hard
stream processingcount-min sketchwindows

Design live comments

hard
fan-outSSEhot streams

Design YouTube

hard
upload pipelineCDNtranscoding

Design Uber

hard
geo-indexmatchinghot cells

Design a payment system

hard
ledgeridempotencyreconciliation

Design Google Docs

hard
OT vs CRDTpresenceversioning

Your first outage is waiting.

We are opening the platform in waves. Join the waitlist and we will email your invite when your spot opens.

One email per person. No spam - just your invite when we launch.