Learn programming, practise on real problems, build projects
ProgrammersOS brings lessons, 250+ practice problems, courses with certificates, a browser workspace and a developer community into one account. It is free to start.
- Practice problems
- 250+
- Courses
- 11
- Career roadmaps
- 13
- Programming languages
- 16
Learn and practise
Understand a topic, apply it on a problem, then come back to it on a schedule. Each part links to the next.
Learn
80+ topics, each with lessons that combine explanations, code examples and links to practice. Mark a lesson complete and it counts toward your progress and badges. Roadmaps lay out 13 developer paths step by step and point to the lessons, courses and problems that cover each step.
Courses
11 structured courses with modules and activities: lessons, quizzes and coding tasks. Some end with a capstone project built in the workspace. Finishing a course earns a certificate you can download as PDF, PNG or JPG, and anyone can check it on the verification page.
Problems
250+ problems, each with a permanent number that never changes. Open one to get a full-screen editor with Run for the examples and Evaluate for a graded submission. Solved problems come back for revision after 3, 7, 15, 30 and 90 days so the patterns stay fresh.
Challenges
260+ short interactive exercises. Take the daily challenge, a random one, or a practice session: quick, one topic, a 60-second speed round, mixed, or a 20-question assessment. Scenario simulators let you work through realistic engineering situations.
How it works
You can read everything without signing in. An account adds submissions, saved progress and AI.
Step 1
Pick a starting point
Choose a roadmap for the role you want, or open a course or topic. Lessons, problems and challenges are readable without an account.
Step 2
Practise and run code
Solve problems in the editor, run code in the compiler, or build in the workspace. Create a free account to submit solutions and save progress.
Step 3
Track progress
Solves, lessons and challenges earn XP. Levels, badges, streaks and the revision schedule show what to do next.
Write code in the browser
Example programs with their output. Open the compiler to run your own.
# Level-Order Binary Tree BFS Traversal
from collections import deque
class TreeNode:
def __init__(self, val=0, left=None, right=None):
self.val, self.left, self.right = val, left, right
def level_order(root):
if not root: return []
res, q = [], deque([root])
while q:
level = []
for _ in range(len(q)):
node = q.popleft()
level.append(node.val)
if node.left: q.append(node.left)
if node.right: q.append(node.right)
res.append(level)
return res
root = TreeNode(1, TreeNode(2), TreeNode(3, TreeNode(4), TreeNode(5)))
print("Level-Order Traversal:", level_order(root))Level-Order Traversal: [[1], [2, 3], [4, 5]]
Compete, discuss and find work
Practice connects to the people around it: contests, a community, articles, career tools and an AI assistant.
Competitions
Coding contests and hackathons with registration, teams, submissions and published results. Each has its own leaderboard, and My competitions tracks everything you have joined.
Community and articles
Ask questions, discuss lessons and problems, and follow tags. Posts get likes and comments, and you can mention members with @username. Write long-form articles with headings, tables, images and code blocks.
Career
Search jobs, track applications, analyse a resume with AI, write cover letters, build a career portfolio and practise with mock interviews. Organizations post the jobs and run hiring.
AI chat
A full assistant with saved conversations and modes for tutoring, coding, code review, debugging, hints only, career advice and study plans. Short answers from the small assistant in the corner of every page do not use credits.
Organizations and classes
Organization accounts manage projects, teams, jobs, assessments, competitions, hackathons and events. Classes bring a group of learners together on the same material.
Build, run and trade
Separate apps on the same account for building projects and finding resources.
Workspace
A cloud project editor with files, code execution and an AI assistant. Course capstone projects open here.
Compiler
A quick online editor that runs code in 16 languages without creating a project.
Tools
Developer utilities for everyday debugging, such as a JSON formatter and diff, a regular expression tester and a JWT inspector.
Marketplace
Templates and starter kits, services from members such as code reviews and mentoring, and open issues from projects that members can take on for XP. Orders are held in escrow until delivery is accepted.
Leaderboard
Developers ranked by XP from problems, challenges, course activities and contests. Levels run from Beginner to Grandmaster.
Frequently asked questions
Is ProgrammersOS free?
Yes. Lessons, practice problems, courses, roadmaps and the developer tools are free to use. Running code and AI features need a free account and have a daily limit. Everyone is on the Free plan while billing is off, which includes 500 AI credits a month.
Do I need an account?
Reading lessons, problems, courses, articles and community posts is open to everyone. Solving problems, posting, saving progress and the AI features need a free account, and email sign-ups confirm their address first.
How are problems graded?
Every problem has a permanent number. Run asks the AI to predict your output on the examples, and says plainly that nothing was executed. Evaluate is a graded submission: an AI traces your code on the hidden tests of the problem, or reviews it against the statement when it has none.
How does the revision list work?
When you solve a problem it gets a review date, and you can mark any problem for revision. A solved problem returns after 3, 7, 15, 30 and 90 days; press Revised each time to move it to the next step.
What do the roadmaps cover?
There are 13 curated career roadmaps: AI & Machine Learning Engineer, Frontend Developer, Backend Developer, Full-Stack Developer, Flutter & Mobile Developer, DevOps Engineer, Cybersecurity & AppSec Engineer, Data Scientist, Data Engineer, Game Developer (C++ & Unreal), Computer Science Fundamentals, Interview Preparation by Pattern, Python Developer. Each one breaks the path into phases of milestones with prerequisites, estimated hours, and links to the courses, lessons and practice on ProgrammersOS that cover them, or to the AI tutor where a lesson does not exist yet.
How does the leaderboard work?
Solving a problem awards XP based on its difficulty, and the problem of the day is worth three times as much. Hints and AI help lower the XP for that solve, and viewing the official solution earns none. Challenges, course activities and contests also award XP. The leaderboard ranks developers by XP over the last week, the last month and all time.
Can I get a certificate?
Yes. Finishing a course earns a certificate that you can download as PDF, PNG or JPG. Anyone can confirm it is genuine on the verify page by entering its certificate ID.
Can I show my work to employers?
Your public profile at /u/your-username lists your level, XP, badges, solve stats, articles and certificates. Privacy switches in Settings hide any section you prefer not to share.
Start with one lesson or one problem
Create a free account to save progress, run code and earn XP, or keep reading without one.