Lessons you actually type. A community you can ask for help.
And real experience building as a team.
An online programming school of 72 modules.
4peiron covers the whole road from complete beginner to professional. Start with free courses that run entirely in your browser, and when something trips you up, ask the community. Join the Team Development plan and you come away with experience worth putting in a portfolio.
Written under the eye of engineers working in the field, in Japan and abroad. Rather than skimming whatever is fashionable, it teaches the shape the work actually takes — code review, agile practice and all.
From “your first web page” to 3DCG and security — a curriculum of 72 modules.
The definitive fifty lessons, from setting up your environment to working professionally. Variables, control flow, data structures, functions, exceptions, files, classes, generators and debugging — with hands-on projects.
50 lessons + 4 projects (all 50 lessons available)
The structure of HTML, layout and styling with CSS, and DOM manipulation with JavaScript. The foundation of web development you want in place before any framework.
HTML/CSS + JavaScript (70 lessons available so far)
From zero to professional Java developer. Fifty lessons covering syntax, object orientation, exceptions, collections, lambdas and streams, finishing with a to-do app that saves to a file.
All 50 lessons available
Twenty lessons that build one complete task management app in Spring Boot, from setting up your environment to deploying to production. DI, Spring Data JPA, N+1, transactions, testing, Thymeleaf, Spring Security, Flyway and Docker, all in one run.
All 20 lessons available
Twenty lessons that build one complete library management app with JSP and Servlets, from standing up Tomcat to deploying a war. Servlet lifecycle, what a JSP really is, MVC Model 2, JDBC, DAOs and CSRF protection — nothing hidden.
All 20 lessons available
Twenty lessons that build one complete blog app in Django, from setting up your environment to deploying to production. Models, the ORM, the admin site, forms, authentication, testing and a REST API, all in one run.
All 20 lessons available
The definitive fifty lessons, from setting up your environment to working professionally. Variables, control flow, ownership and borrowing, data structures, functions, error handling, structs and traits, Cargo and debugging — with hands-on projects.
50 lessons + 4 projects (all 50 lessons available)
The definitive fifty lessons, from cleaning data to working professionally. NumPy, pandas, visualisation, preprocessing, regression, classification, model evaluation, clustering, PyTorch and LLMs — with hands-on projects.
50 lessons + 4 projects (all 50 lessons available)
Twenty lessons that build one complete recipe-sharing app in Next.js, from setting up your environment to deploying to production. App Router, Server Components, Server Actions, Prisma, authentication and Cache Components, all in one run.
All 20 lessons available
The definitive forty lessons on turning your shell, editor and multiplexer into a single working environment. Configuring fish and its completions, Neovim motions, Lua config and LSP, tmux session management, dotfiles, and writing your own additions in Lua.
All 40 lessons available
Add types to JavaScript and catch your mistakes before you run anything. Fifty lessons from type annotations and inference through to generics, utility types, type guards, async code and the DOM.
All 50 lessons available
The definitive course on server-side JavaScript. Fifty lessons on async code, file I/O, HTTP, Express and SQLite, finishing with a notes API and a CLI.
All 50 lessons available
Twenty lessons that build one complete task management API in FastAPI, from setting up your environment to deploying to production. Validation from type hints, dependency injection, SQLAlchemy 2.0, JWT authentication, pytest and Docker, all in one run.
All 20 lessons available
Thirty lessons on Git and GitHub, from your first commit to contributing to open source. Branches, merges, resolving conflicts, pull requests, reviews, Actions CI and Pages — with the real command output and error messages you will see.
All 30 lessons available
Swift without Xcode. Fifty lessons on syntax, optionals, structs and protocols, error handling and async/await, finishing with a task manager that saves to JSON.
All 50 lessons available
Twenty lessons treating Blender as a 3D engine you drive from Python. Headless execution, modelling, materials, lighting, rigging, add-ons and batch rendering from the CLI.
All 20 lessons available
The definitive fifty lessons, from setting up your environment to working professionally. Files, text processing, permissions, how the shell works, processes and systemd, networking and shell scripting — with hands-on projects.
All 50 lessons available
Thirty lessons on security with Python, from where the ethical and legal lines sit to defending against web vulnerabilities. Port scanning, hashing and encryption, log analysis, SQLi, XSS and CSRF — all against your own local lab and nothing else.
All 30 lessons available
Twenty lessons that build one complete CLI against the Spotify Web API, from registering the app through OAuth (PKCE), rate limits, playlist operations, an SQLite cache, testing and scheduled runs. Written around the major API changes of November 2024 and February 2026, so it only teaches what works today.
All 20 lessons available
The definitive fifty lessons, from setting up your environment to working professionally. Slices and maps, structs and interfaces, error handling, splitting packages, generics, goroutines and channels, and testing — with hands-on projects.
All 50 lessons available
The definitive twenty lessons, from installing Docker to working professionally. Images and containers, ports and networks, volumes, Dockerfiles, multi-stage builds and Docker Compose — with troubleshooting.
All 20 lessons available
Twenty lessons on Scrum, taught with seven sprints of real data from a fictional team. Writing the backlog, relative estimation, reading burndown charts and velocity, the definition of done, Monte Carlo forecasting and spotting anti-patterns — every lesson reads one more number.
All 20 lessons available
Twenty lessons that let you explain why something is slow. From measuring complexity for real to binary search, sorting, hash tables, heaps, graph traversal, dynamic programming and greedy algorithms. Every lesson runs the code and times it (brute force vs. a hash: 1,058x; naive recursion vs. memoisation: about 40,000x).
All 20 lessons available
From bits and binary to adders, CPUs, databases, networks and the cloud. Rather than memorising terms, all twenty lessons run real code and confirm what happened in numbers and bytes. It also lays the groundwork for Japan's Fundamental IT Engineer Examination.
All 20 lessons available
Linux from the side that looks after the server. The design of root and sudo, package management, boot and GRUB, systemd, logs, cron, storage and backups. You build one practice environment you are allowed to break, then do everything you could never try in production there.
30 lessons (30 lessons available so far)
Thirty lessons that carry one project — an equipment lending system — all the way from proposal to operation. Instead of a disconnected example per phase, you see how a decision made during requirements plays out in design, testing and migration, confirmed in numbers every time.
All 30 lessons available
Networking is hard because you have no network in front of you. So we build one. Inside a single container you stand up three hosts and two routers, then work through subnet masks, routing tables, NAT, TCP, DNS, IPv6 and firewalls by breaking things and seeing what happens.
30 lessons (30 lessons available so far)
Turn the procedure you have been copy-pasting into a script you can hand over. Why quoting breaks things, what set -euo pipefail actually stops, how to clean up with trap, and how ShellCheck and bats keep it safe.
20 lessons (20 lessons available so far)
A course that hunts down the bugs which slipped past "I checked that it works", one technique at a time. Six defects are seeded, and each one is built so that the previous lesson's technique cannot find it.
20 lessons (20 lessons available so far)
Not vocabulary drills: a measured look at what you are billed for, where things get slow and where they break. No account required. It ends with you designing one small service.
20 lessons (20 lessons available so far)
Where exactly does docker compose stop being enough? You build one cluster locally with kind, put your own app on it, kill it, update it and expose it. The same app grows across all twenty lessons.
20 lessons (20 lessons available so far)
Move from "I can write SQL but I am not sure" to "I can explain the result". The MySQL and PostgreSQL courses follow the same running order, so whichever you start with, the other reads as a diff.
MySQL + PostgreSQL (60 lessons available so far)
From hashing to the EVM, this 30-lesson course builds Bitcoin and Ethereum from scratch. You'll implement elliptic curves, ECDSA signatures, proof-of-work, UTXO transactions, and the smart contract virtual machine yourself, using only Python's standard library — no web3, no bitcoinlib.
All 30 lessons available
A 20-lesson course on building desktop, web, and mobile apps with nothing but Python. From controls and layout to declarative code with component and use_state, routing, theming, persistence, external APIs, charts, and distributing with flet build. Across all 20 lessons, you'll build one household budgeting app from start to finish.
All 20 lessons available
The definitive guide from Unity Hub install to Steam publishing across 50 lessons. WheelCollider vehicle physics, engine and gear ratios, Cinemachine and HUD, Spline road generation, URP night scenes, AI rival cars, optimization, and Steamworks.NET with practical projects.
All 50 lessons available
50 lessons that take you from prompt design through tool use, RAG, and production operations using a local LLM (Ollama) on your own machine — no paid API key required. Built around public automotive data, you'll finish by shipping a complete FastAPI vehicle-info assistant.
All 50 lessons available
React without frameworks across 50 lessons, running with Vite. Master JSX, props, state, useEffect, hooks, React Router, testing, and finish by building and publishing a task app.
All 50 lessons available
From writing your first workflow to automating tests, releases, and server deploys — a 20-lesson introduction to GitHub Actions. Covers matrices, caching, Secrets, OIDC, rollbacks, and reusable workflows, with output actually run through act.
All 20 lessons available
From Kotlin syntax to Jetpack Compose UI, ViewModel, Room, Retrofit, and signing for Play Console — 50 lessons build complete Android apps. Grow the memo screen from lesson 30 into a finished memo app by lesson 50.
All 50 lessons available
The definitive guide to C# itself before Unity. Learn types and object-oriented programming, records and pattern matching, LINQ, async/await, xUnit, and Minimal API across 50 lessons, then bridge to Unity's C#.
All 50 lessons available
Write raw PHP first, then enter Laravel 13, and publish a membership app with Docker — 50 lessons throughout. Write forms, sessions, PDO, SQL injection defenses yourself, then move to routing, Blade, Eloquent, authentication, queues, and APIs.
All 50 lessons available
Write infrastructure as code instead of clicking through a console, and read the plan before you apply it. Across 20 lessons, you'll work through HCL, tfstate, modules, VPC and IAM, CI review, and drift — no AWS account required.
All 20 lessons available
The definitive guide from compilation to system calls across 50 lessons. Learn pointers, malloc and free, sanitizers and valgrind, structs and linked lists, make and libraries, and finish by building a simple shell.
All 50 lessons available
30 lessons that turn working code into code that's readable and easy to change. From naming and early returns to SOLID, dependency injection, characterization tests, and ADRs, each lesson lines up a before and after in Python and Java.
All 30 lessons available
Three.js, for rendering 3D in the browser, from your first scene to publishing it — across 20 lessons. Covers lighting and PBR, bringing in glTF models from Blender, mouse controls, Bloom, and optimization.
All 20 lessons available
An introduction to Vue 3 (Composition API), running everything through Vite across 30 lessons. Covers template syntax, ref, props and emit, Vue Router, Pinia, and testing, wrapping up by clarifying how it differs from React.
All 30 lessons available
An entry point into UI/UX design that starts without writing any code, across 20 lessons. From the principles of spacing, typography, and color to Figma's Auto Layout and components, design tokens, and usability testing, you'll verify what makes design good or bad using real numbers.
All 20 lessons available
A hands-on, 30-lesson data analysis course that takes you from framing the right question to making a decision. Covers SQL extraction, pandas data wrangling, visualization, and standard analyses like cohorts and A/B testing, with practical exercises throughout.
All 30 lessons available
An intro to authentication that builds a membership site's login end-to-end over 30 lessons, from storing passwords to social login and plan management. Verify sessions, CSRF, OAuth 2.0, rate limiting, two-factor authentication, and audit logging by actually running them in Django tests.
All 30 lessons available
An intro to adding Stripe recurring billing to Django over 30 lessons, from a design that never touches card data to switching to production. Covers Checkout, Webhook signature verification and idempotency, failed payments and cancellations, and the customer portal — all verified locally without any real keys.
All 30 lessons available
50 lessons that take a service you've built, put it on a VPS costing a few dollars a month, and keep it running in production. From hardening SSH, Docker Compose, and Caddy's TLS, through the first deploy, all the way to backup and restore, rollbacks, and a maintenance page.
All 50 lessons available
The definitive 50-lesson course for people who already know C. Work through classes and RAII, the STL, templates, smart pointers, ranges, and threads, and finish by building a complete tool with CMake and tests.
All 50 lessons available
30 lessons on writing code together with AI. Covers how to write instructions, set up your repository, read diffs, and constrain work with tests, plus where to draw the line on work you must not hand off.
All 30 lessons available
30 lessons on framework-independent API design, from the promises at your boundary to retiring old versions. You'll decide on URLs and status codes, a unified error format, idempotency and retries, OpenAPI, and GraphQL, all while running them on plain HTTP.
All 30 lessons available
An introduction that takes you from Ruby syntax all the way to building and launching a members-only blog, across 50 lessons. It covers MVC, Active Record, forms and authentication, RSpec, and Hotwire, and finishes by deploying with Docker and Kamal.
All 50 lessons available
50 lessons on shipping to iOS, Android, and the web from a single codebase. From Dart syntax through widgets and layout, state management with Riverpod, networking and storage, testing, and signing and store submission. This is Flutter written in Dart, not Flet used from Python.
All 50 lessons available
30 lessons on noticing problems in the services you ship before your users do. You'll run structured logs, Prometheus metrics, Grafana dashboards, Alertmanager notifications, and OpenTelemetry distributed tracing on your own machine, all the way through to SLOs and error budgets.
All 30 lessons available
50 lessons that bridge the gap between the Machine Learning and AI Apps courses. From tensors and automatic differentiation to implementing CNNs and Transformers yourself, all the way to shipping them as ONNX and an API. Every output was actually measured on PyTorch 2.14.0.
All 50 lessons available
30 lessons that fill in where an RDB alone struggles. Redis types and TTLs; caching, sessions, rate limiting, and queues; and on to MongoDB document design, all backed by real measurements.
All 30 lessons available
20 lessons to take after HTML/CSS for Beginners. From custom properties, Grid, container queries, and :has() to design tokens, architecture, and hands-on measurements of Tailwind CSS v4.
All 20 lessons available
The definitive 20-lesson guide, from assistive technology and WCAG to semantic HTML, ARIA, focus management, and contrast. You'll verify roles, names, and states by pulling up Chrome's accessibility tree, and see the limits of automated checks by actually running axe-core, pa11y, and Lighthouse.
All 20 lessons available
From strings of bits to the CPU, memory, processes, and I/O, 30 lessons that measure and confirm "what's actually happening inside." You'll follow arm64 assembly, caches, page faults, fork and exec, and race conditions, all through the output of code that was actually run.
All 30 lessons available
30 lessons that fill in the foundations for machine learning, deep learning, and data analysis. You'll get a feel for exponents and logarithms, vectors and matrices, derivatives and gradient descent, and probability and statistics by working hands-on in Python rather than through proofs.
All 30 lessons available
30 lessons that continue from Algorithms for Beginners. You'll learn complexity estimates, brute force, binary search and prefix sums, dynamic programming, and graph techniques, every time through exercises in the form "task → implementation steps → sample solution → extra challenges."
All 30 lessons available
20 lessons on turning what you've learned into a job. From choosing a project and estimating its size, to finishing it, publishing, writing a work history document (shokumu keirekisho), coding tests, and your first three months on the job. We skip generalizations we can't back up and cover only what you can verify with commands on your own machine.
All 20 lessons available
Over 20 lessons, learn the patterns behind the things you write every day at work: READMEs, commit messages, PR descriptions, design notes, runbooks, and incident reports. Good examples are quoted from a real service's docs, and each chapter has exercises fixing bad writing.
All 20 lessons available
The third option, neither React nor Vue: the definitive guide in 30 lessons. Cover the compiler's output, Runes, SvelteKit routing and load, form actions, testing, and adapters, and finish by laying React, Vue, and Svelte side by side to sort out how to choose.
All 30 lessons available
20 lessons you can jump into right after HTML/CSS basics. If the writing comes first, choose Astro; if you need logins and a database, choose Next.js. You'll draw that line by building the same page and comparing how many bytes of JavaScript each one serves.
All 20 lessons available
30 lessons for people who know React to move straight into mobile. Core components and styles, Expo Router, the camera, location and notifications, storage, testing, and release builds, all actually run on Expo SDK 57.
All 30 lessons available
The definitive 30-lesson course, from launching the editor to publishing on the Web. Cover scenes and nodes, GDScript, CharacterBody2D and signals, TileMapLayer, HUDs and save data, a first look at 3D, and exporting, and finish a complete 2D game. A lightweight starting point for anyone who finds Unity too heavy.
All 30 lessons available
30 lessons that show what happens the moment a system splits into multiple services, by actually running Kafka and multiple processes. You'll work through drawing boundaries, timeouts and retries, topics and offsets, and sagas and the outbox, and finish with the decisions "don't split" and "merge back."
All 30 lessons available
Learn Lua, the language embedded in Neovim, LÖVE, and Redis, from the ground up in 20 lessons. Cover tables and metatables, closures and coroutines, and _ENV sandboxes, and finish by having a C host load Lua plugins.
All 20 lessons available
From your first steps to skills you use at work. Languages, web technology and infrastructure, with new courses added over time.
Stuck on something? Ask in our Discord community. Mentors and fellow learners work it out with you, so it is much harder to give up.
A quiz per lesson settles what you learned, shows you the weak spots and moves you up.
Join a real project and absorb a professional eye through code review — a strong card when you go job hunting.
The name comes from the Ancient Greek ἄπειρον (apeiron) — “the boundless, the infinite”. The philosopher Anaximander gave that name to the source everything arises from. Learning has no end either, and the range of code you can write keeps widening — so we swapped the leading “a” for “4 (for)”: that boundlessness, opened up for you. That is the idea this school was built on.