Challenge Library
Coding Challenges
5,893 curated questions across every arena — browse by topic, then jump into a live 3-minute battle to put them to the test.
Filter by type
Filter by difficulty
Popular topics
732 challenges matching your filters
Clear topic filter- Code AnalysisHard
Trace: Lost Update
backendanalysishard - Code AnalysisHard
Trace: Retry Storm
backendanalysishard - Code AnalysisHard
Idempotency key flow
backendhard - Code AnalysisHard
Circuit breaker states
backendhard - Code AnalysisHard
Circuit breaker flow
backendhard - Code AnalysisHard
Service discovery flow
backendhard - Code AnalysisHard
Saga orchestration
backendhard - Code AnalysisHard
Refresh token rotation
backendhard - Code AnalysisHard
Cache stampede prevention
backendhard - Multiple ChoiceHard
Index Types
backendhard - Multiple ChoiceHard
1NF, 2NF, 3NF
backendhard - Multiple ChoiceHard
Isolation Levels
backendhard - Code AnalysisHard
Normalization 2NF
backendhard - Multiple ChoiceHard
GitOps
backendhard - Multiple ChoiceHard
Immutable Infrastructure
backendhard - Multiple ChoiceHard
Liveness vs Readiness
backendhard - Multiple ChoiceHard
ArgoCD
backendhard - Code AnalysisHard
Readiness probe
backendhard - Multiple ChoiceHard
Chain of Responsibility
backendhard - Multiple ChoiceHard
Event Sourcing
backendhard - Multiple ChoiceHard
CQRS Pattern
backendhard - Multiple ChoiceHard
Clean Architecture
backendhard - Multiple ChoiceHard
DDD Aggregates
backendhard - Code AnalysisHard
Event sourcing replay
backendhard - Code AnalysisHard
Clean arch dependency rule
backendhard - Code AnalysisHard
Aggregate root
backendhard - Multiple ChoiceHard
Server-Sent Events
backendhard - Multiple ChoiceHard
API throttling
backendhard - Multiple ChoiceHard
Hypermedia API advantages
backendhard - Multiple ChoiceHard
HTTP/3 (QUIC)
backendhard - Multiple ChoiceHard
SSE vs WebSocket
backendhard - Multiple ChoiceHard
Vary header
backendhard - Multiple ChoiceHard
Window functions
backendhard - Multiple ChoiceHard
Database locking
backendhard - Multiple ChoiceHard
Full-text search
backendhard - Multiple ChoiceHard
Materialized views
backendhard - Multiple ChoiceHard
Query plan analysis
backendhard - Multiple ChoiceHard
OAuth implicit flow
backendhard - Multiple ChoiceHard
HMAC
backendhard - Multiple ChoiceHard
XXE attack
backendhard - Multiple ChoiceHard
SSRF
backendhard - Multiple ChoiceHard
Insecure deserialization
backendhard - Multiple ChoiceHard
Service mesh
backendhard - Multiple ChoiceHard
Sidecar pattern
backendhard - Multiple ChoiceHard
GitOps workflow
backendhard - Multiple ChoiceHard
Chaos engineering
backendhard - Multiple ChoiceHard
Log drivers
backendhard - Multiple ChoiceHard
Event sourcing benefits
backendhard - Multiple ChoiceHard
Saga vs 2PC
backendhard - Multiple ChoiceHard
Data warehouse vs OLTP
backendhard - Multiple ChoiceHard
Concurrency control
backendhard - Multiple ChoiceHard
Master election
backendhard - Multiple ChoiceHard
Quorum
backendhard - Multiple ChoiceHard
Backpressure strategies
backendhard - Multiple ChoiceHard
Circuit Breaker — Half-Open State
backendhard - Multiple ChoiceHard
Bulkhead pattern
backendhard - Multiple ChoiceHard
HATEOAS
backendhard - Multiple ChoiceHard
Disaster Recovery
backendhard - Multiple ChoiceHard
Prometheus Metrics Types
backendhard - Multiple ChoiceHard
SLO/SLI/SLA
backendhard
Practice now, dominate the arena
Every challenge here is drawn from the live Code Royale pool. Review a question, then head to the arena to answer under pressure against a real opponent — 3-minute matches, Elo ranking, and badge tiers on the line.