Challenge Library
Coding Challenges
5,893 curated questions across every arena — browse by topic, then jump into a live 2-minute battle to put them to the test.
Filter by type
Filter by difficulty
Popular topics
4,318 challenges matching your filters
- Multiple ChoiceBeginner
Hexagonal architecture: the driving side
hexagonalports-adapters - Multiple ChoiceBeginner
Onion architecture: innermost layer
onionclean - Multiple ChoiceBeginner
Pipe-and-filter: filter contract
pipe-and-filtercoupling - Multiple ChoiceBeginner
Microkernel: plugin isolation
microkernelocp - Multiple ChoiceBeginner
Context mapping: shared kernel risk
dddcontext-mappingshared-kernel - Multiple ChoiceBeginner
Aggregate root: external access rule
dddaggregateinvariants - Multiple ChoiceBeginner
Value object: equality semantics
dddvalue-objectentity - Multiple ChoiceBeginner
Domain event vs integration event
ddddomain-eventsintegration-events - Multiple ChoiceIntermediate
Actor model: no shared mutable state
actor-modelconcurrency - Multiple ChoiceIntermediate
CQRS: separate write and read models
cqrsread-model - Multiple ChoiceIntermediate
Event sourcing: source of truth
event-sourcingcqrs - Multiple ChoiceIntermediate
Saga vs process manager role
sagaprocess-managerevent-driven - Multiple ChoiceIntermediate
Repository vs Unit of Work roles
repositoryunit-of-work - Multiple ChoiceIntermediate
GRASP: Information Expert guidance
graspsrp - Multiple ChoiceIntermediate
Strategy vs Template Method
strategytemplate-methodcomposition - Multiple ChoiceIntermediate
Bridge pattern: separating dimensions
bridgepatterns - Multiple ChoiceIntermediate
Prototype pattern: cloning intent
prototypepatterns - Multiple ChoiceIntermediate
Mediator: reducing many-to-many coupling
mediatorcoupling - Multiple ChoiceHard
Connascence: weakest to strongest
connascencecoupling - Multiple ChoiceHard
Distance from main sequence D
metricsabstractnessdistance - Multiple ChoiceHard
Unstable classes should depend on stable
sdpmetricsstability - Multiple ChoiceHard
Acyclic dependencies: breaking a cycle
acyclic-dependenciescoupling - Multiple ChoiceHard
Architecture quantum and independent deployability
architecture-quantumevolutionary-architecture - Multiple ChoiceBeginner
Anemic domain model symptom
anemic-modelrich-modelanti-pattern - Multiple ChoiceBeginner
Big Ball of Mud root cause
big-ball-of-mudanti-pattern - Multiple ChoiceIntermediate
Cyclic web: shotgun surgery cause
cyclic-dependenciesshotgun-surgeryanti-pattern - Multiple ChoiceIntermediate
Feature flags vs branches trade-off
feature-flagstrunk-basedci - Multiple ChoiceIntermediate
Fitness functions in evolutionary architecture
fitness-functionsevolutionary-architecture - Multiple ChoiceBeginner
ADR: documenting a decision
adrdocumentation - Multiple ChoiceIntermediate
Branch by abstraction vs feature branch
branch-by-abstractionstrangler-fig - Multiple ChoiceIntermediate
Blue-green vs canary deployment
blue-greencanarydeployment - Multiple ChoiceHard
Expand-contract: safe schema evolution
expand-contractschema-evolutionzero-downtime - Multiple ChoiceIntermediate
Test trophy vs test pyramid
test-pyramidtest-trophytesting - Multiple ChoiceBeginner
Null Object vs Optional
null-objectpatterns - Multiple ChoiceHard
Specification pattern reuse
specificationdomain-model - Multiple ChoiceBeginner
Architectural Fitness Functions
fitness-functionsevolutionary-architectureci - Multiple ChoiceIntermediate
Architecture Quantum
architecture-quantumdeploymentcohesion - Multiple ChoiceBeginner
Detecting a Distributed Monolith
distributed-monolithdeploymentcoupling - Multiple ChoiceBeginner
Stable Dependencies Principle
coupling-metricsdependency-graphsolid - Multiple ChoiceBeginner
Walking Skeleton Purpose
walking-skeletonincrementaldelivery - Multiple ChoiceBeginner
API Versioning: URI Path
api-versioningrestcompatibility - Multiple ChoiceIntermediate
HATEOAS Core Idea
hateoasresthypermedia - Multiple ChoiceBeginner
Consumer-Driven Contracts
contract-testingpactcdc - Multiple ChoiceIntermediate
Expand-Contract Migration Pattern
expand-contractdatabasemigration - Multiple ChoiceBeginner
Feature Flag Debt
feature-flagstechnical-debtcleanup - Multiple ChoiceBeginner
Trunk-Based Development
trunk-basedgitflowci - Multiple ChoiceIntermediate
ADR Lifecycle
adrdecision-recordsgovernance - Multiple ChoiceBeginner
ATAM Quality Attribute Scenario
atamquality-attributesscenarios - Multiple ChoiceBeginner
Vertical Slice Architecture
vertical-slicemodularitystructure - Multiple ChoiceIntermediate
Modular Monolith Boundaries
modular-monolithboundariesencapsulation - Multiple ChoiceBeginner
Published Language
published-languagedddintegration - Multiple ChoiceBeginner
Backend for Frontend (BFF)
bffapi-gatewayfrontend - Multiple ChoiceIntermediate
API Gateway vs Service Mesh
api-gatewayservice-meshtraffic - Multiple ChoiceIntermediate
Sidecar vs Library
sidecarservice-meshcross-cutting - Multiple ChoiceHard
Service Mesh mTLS
mtlsservice-meshsecurity - Multiple ChoiceBeginner
Golden Paths
platform-engineeringgolden-pathdx - Multiple ChoiceIntermediate
Team Topologies: Cognitive Load
team-topologiescognitive-loadorg-design - Multiple ChoiceIntermediate
Event Sourcing Snapshotting
event-sourcingsnapshottingperformance - Multiple ChoiceBeginner
Optimistic UI
optimistic-uieventual-consistencyux - Multiple ChoiceBeginner
Offline-first sync: conflict-free field types
offline-firstcrdtconflict-resolution
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 — 2-minute matches, Elo ranking, and badge tiers on the line.