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PrepAIDeveloper and QA prep
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free learning paths, films and practice

Interview preparation for developers and testers, explained step by step

Learn the topics interviewers actually ask about, in the right order. Developers get data structures and algorithms, system design, databases, security, cloud, DevOps and AI; testers get manual and automation testing, API, performance and security testing, and the tools for each. Pick your role once and the site shows the topics that matter to you. Every lesson starts in plain words, then shows how it really works, with diagrams, code in C#, JavaScript and Python, animated films and interview questions with model answers.

75 learning paths
700+ lessons
40+ explainer films
1398+ questions
Covers

What are you preparing for?

Backend engineer

Data structures, databases, APIs, security and the messaging behind them.

  1. Data structures and algorithms
  2. SQL and databases
  3. REST API
  4. Authentication and Authorization
  5. Message queues and brokers
  6. System design

System design interview

The building blocks first, then the patterns, then whole systems.

  1. Networking fundamentals
  2. Performance and caching
  3. Microservices and distributed systems patterns
  4. Kafka
  5. Rate limiting and throttling
  6. System design

Cloud and DevOps

Linux and containers, pipelines, infrastructure as code and running it all in production.

  1. Linux and shell scripting
  2. Docker and Kubernetes
  3. CI/CD pipelines
  4. Terraform and infrastructure as code
  5. Observability and production support
  6. Site reliability engineering (SRE)

AI engineer

How models work, retrieval, building LLM apps and working well with AI coding tools.

  1. AI and LLM
  2. RAG and vector search
  3. Building LLM apps and agents
  4. Claude in Brief
  5. MLOps

Testing as a developer

Unit and integration tests, test doubles, TDD, NUnit, xUnit, JUnit, pytest, Jest and clean, testable code.

  1. Testing and clean code
  2. Unit testing frameworks
  3. Low-level design
  4. REST API
  5. CI/CD pipelines

Tester: the craft

Manual and automation testing, smoke and regression, API, performance and security testing, and the frameworks.

  1. Software testing and QA fundamentals
  2. Test automation
  3. API testing
  4. Performance testing
  5. Specialised testing
  6. Unit testing frameworks

Tester: cloud, DevOps, AI and data

Testing cloud environments, pipelines and containers, AI and LLM features, microservices, events and data pipelines.

  1. Testing cloud applications
  2. Testing in DevOps and CI/CD
  3. Testing AI and LLM applications
  4. Testing microservices, events and data
  5. CI/CD pipelines
  6. Docker and Kubernetes

Core skills for a developer

9 lessons
Data structures and algorithms

A nine-lesson route from Big-O and arrays to graphs and dynamic programming, with Python and JavaScript code you can…

11 lessons
System design

An eleven-lesson route through estimation, caching, sharding, consistency, messaging and reliability, ending with full…

12 lessons
C# and .NET

A twelve-lesson route through modern C# and .NET 8, covering the language, async, memory, ASP.NET Core, EF Core,…

11 lessons
SQL and databases

Learn to query, join, aggregate, design, index and tune relational databases, then practise the problems interviewers…

9 lessons
Networking fundamentals

A nine-lesson route through the networking knowledge developers use at work and are asked in interviews, with real…

10 lessons
Operating systems

A ten-lesson route from what the kernel gives each process and thread to virtual memory, locks, I/O models and…

9 lessons
Authentication and Authorization

A nine-lesson route from passwords and cookies to JWT, OAuth with PKCE, OIDC, passkeys, RBAC and ABAC, and securing…

9 lessons
Microservices and distributed systems patterns

A nine-lesson route through the patterns asked in senior backend and system design interviews, with diagrams, copyable…

11 lessons
Kafka

An eleven-lesson route through the Kafka concepts used at work and asked in interviews, with real CLI commands, client…

11 lessons
Docker and Kubernetes

Containers, Dockerfiles, Compose, then Kubernetes objects, config, scaling and the debugging flow interviewers ask…

10 lessons
AI and LLM

Learn how large language models work and how to build, test and run reliable applications on top of them.

14 lessons
Claude in Brief

A fourteen-lesson, implementation-focused route through Claude Code: the agent loop, Plan Mode, CLAUDE.md,…

Browse every topic by category

Core skills

Start here: version control, the command line, networks, databases and algorithms. Everything else builds on…

All 6

Languages and frameworks

Pick the stack you work in, then add the others.

All 10

Data, storage and streaming

How data is mapped, cached, searched, streamed and processed at scale.

All 10

APIs and integration

How services talk to each other and to the outside world.

All 5

Testing your code

For people who write the code: unit and integration tests, test doubles, TDD, flaky tests, coverage and…

All 1

Testing and QA

Manual testing, the kinds of test (smoke, sanity, regression), automation, API, performance, mobile and…

All 10

Security and identity

Who is calling, what they may do, and how to keep the system safe.

All 2

Architecture and design

Put the pieces together: scale, reliability and trade-offs.

All 6

DevOps and delivery

Package, test and ship software safely and often.

All 7

Cloud platforms

Run it on a major cloud. One is enough to start; the ideas carry across.

All 7

Observability and operations

See what production is doing and fix it fast.

All 4

AI and machine learning

Large language models and the engineering around them.

All 6

Career and interviews

The non-code half of getting hired: resume, behavioural answers, interview strategy, offers and growth.

All 1

Practise and revise

Explainer films

Short narrated animations: process vs thread, JWT, Kafka groups, indexes, TCP, RAG and more.

Algorithms in motion

Watch sorting, BFS, DFS and Dijkstra run, with C#, JavaScript and Python code.

Coding questions

Interview problems with several solutions and animated walkthroughs.

System design questions

Step-by-step answers with diagrams, from a URL shortener to ad click aggregation.

Tech FAQs

Quick interview questions and answers by technology.

Cheat sheets

One-page printable references, from Git and SQL to Claude Code and operating systems.

Mock interview

Practise out loud with an AI interviewer and get feedback.

Quizzes

Multiple-choice practice for every learning path, with explanations.

New on PrepAI

New course
Claude in Brief: learn Claude Code properly

A 14-lesson course on Claude Code and AI-assisted engineering: plan mode, CLAUDE.md, permission modes, hooks, GitHub Actions,…

New path
Operating systems, explained with pictures

Ten lessons from processes and threads to containers, each with an animated film. Start with the process vs thread film: what…

Watch
40+ animated explainer films

Short narrated films that build a diagram piece by piece: Kafka consumer groups, JWT vs sessions, database indexes, TCP, RAG,…

See everything that is new

The full list of recent topics, films and walkthroughs, newest first.

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