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Updated for .NET 10 & C# 14
Understand .NET.
Prepare for your next interview.
A bilingual study and review guide for Junior, Mid and Senior .NET developers. Start with the problem and a practical example, then check your understanding with 585 interview questions and 370 quiz questions.
35Topics
585Interview questions
370Test yourself
Junior 171Mid 265Senior 149
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1. Understand the ideaRead the topic introduction and practical problem before the code. Follow the prerequisite links when a term is unfamiliar.
2. Trace the example and answerFollow the inputs and outcome, and explain why the solution fits. Answer interview questions yourself before opening the model answer.
3. Check and return laterYour reading position and answers are saved in this browser. Use “Continue where you left off” on return. Completed topics and quiz scores are separate.
Start at your level
Choose a starting point, then revisit any topic you need. Levels are a guide.
Junior
Build your foundations and run the examples yourself.
Mid
Review everyday implementation choices and failure cases.
Senior
Practice decisions, constraints and design trade-offs.
The interview
C# & .NET
02C# fundamentals & OOPTypes, OOP, class vs struct vs record, interfaces, ref/out, decimal, generics, delegates, exceptions.03.NET runtime: CLR, JIT & GC.NET Framework vs .NET 10, CLR and IL, JIT types, tiered PGO, AOT, GC, IDisposable, memory leaks.04Async & multithreadingThread vs Task, async/await internals, WhenAll, cancellation, locks, race conditions, deadlocks.05LINQ & collectionsIEnumerable vs IQueryable, Dictionary and HashSet, deferred execution, SelectMany, GroupBy.06C# 14, .NET 10 & performanceWhat's new in C# 14 and .NET 10, old-vs-new comparisons, Span, source generators, BenchmarkDotNet.
Web & APIs
07ASP.NET Core & MVCMVC, Kestrel, middleware, routing, model binding, filters, DI, configuration, CORS.08Web APIs, REST & gRPCREST, status codes, idempotency, pagination, versioning, OpenAPI, gRPC, SignalR.
Data & databases
09Entity Framework CoreDbContext, tracking, loading strategies, N+1, migrations, concurrency, Dapper, performance.10SQL & databasesJoins, GROUP BY, window functions, indexes, normalization, ACID, NoSQL, practice queries.11NoSQL & data modelingDocument, key-value, wide-column and graph stores, MongoDB, Redis, Cassandra, Cosmos DB, sharding, replication, SQL vs NoSQL.12Data consistency & transactionsIsolation anomalies, MVCC, locking, replication, consistency models, distributed transactions.13Relational algebra & database theoryBonusSelection, projection, joins, how they map to SQL, the query optimizer, functional dependencies, keys.
Design & architecture
14SOLID & architectureSOLID, Clean Architecture, vertical slices, DDD, modular monolith, microservices, CQRS.15Design patternsAll 23 GoF patterns in C#, plus Repository, Unit of Work, Specification and Result.16Clean code & refactoringNaming, functions, DRY/KISS/YAGNI, code smells, refactoring techniques, code review.
Distributed systems
17Messaging & distributed systemsMessage brokers, RabbitMQ, Kafka, outbox, idempotency, sagas, resilience.18Caching & RedisIMemoryCache, Redis, HybridCache, output caching, invalidation, stampedes.
Quality & operations
19SecurityAuthN vs AuthZ, OAuth2/OIDC, JWT, passkeys, OWASP Top 10, secrets.20Logging & observabilityStructured logging, OpenTelemetry, metrics, traces, health checks, production debugging.21TestingUnit vs integration, xUnit v3, mocking, WebApplicationFactory, Testcontainers, TDD.22Docker, CI/CD & GitDockerfiles, Compose, Kubernetes, GitHub Actions, Git, zero-downtime deployment.23Cloud fundamentalsIaaS, PaaS, SaaS, Azure and AWS services, serverless, storage, scaling, cost, infrastructure as code.
Engineering foundations
24HTTP & networkingThe life of a request, DNS, TCP, TLS, HTTP/1.1 vs 2 vs 3, headers, cookies, proxies.25Operating system fundamentalsBonusProcesses vs threads, context switching, virtual memory, I/O models, scheduling.26Legacy systems & integrationsSOAP/WCF, anti-corruption layers, strangler fig, migrating from .NET Framework.27The software engineering processSDLC, Agile, Scrum and Kanban, estimation, requirements, documentation, technical debt, definition of done.
Problem solving
28Data structures & algorithmsBig-O, arrays and linked lists, hash tables, trees, graphs, sorting, dynamic programming.29Coding problems, solvedClassic interview problems with explained C# solutions, complexity and thinking aloud.
AI
30AI in .NET: RAG, embeddings & MCPBonusMicrosoft.Extensions.AI, RAG, embeddings, MCP, agents, safety.31Directing and reviewing AISpec-driven development, reviewing plans, a checklist for AI-written code, its classic .NET mistakes.
System design & career
32System designA framework for answers, scaling, caching, queues, multi-tenancy, worked examples.33Behavioral & careerSTAR, code review, mentoring, conflict, questions to ask, salary negotiation.
Bonus: optional but valuable
Final exam
Sayed Elmahdy
Software Engineer (.NET). I collected these questions from real interviews and production work, and I keep them current with every .NET release.