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Python · JavaScript · SQL · nothing to install

Anyone can ask an AI for code.
Few can tell if it’s right.

Learn to code and be one of the few. Short lessons, real challenges and a profile that climbs the ranks like the industry does: from Student to Principal.

Start in your browserSee a lesson
359
lessons written
382
challenges with tests
8
career ranks

How you learn

You do not read code. You write it.

Every lesson is 8 to 12 exercises of five minutes each. The code really runs inside the app: if your answer produces the right result, it is right.

Predict the output

print("Hello")
print("world")
Hello world
Hello world

You read the program and say what it prints, before running it.

Put the code in order

age = 20
if age >= 18:
print("You can vote")
print("Not yet")

Drag the lines around until the program does what the exercise asks for.

Find the bug

def average(a, b):
return a + b / 2
print(average(8, 10))

Line 2

The division happens before the addition. It needs parentheses: (a + b) / 2

You also practise withfill in the blankmatch the pairswrite the unit project

Uptime

One day at a time. No punishment.

Uptime counts the days in a row you keep the service up. If one day you cannot, a hotfix covers it. There are no lives and no hearts to lose here: the question you get wrong simply comes back.

2 hotfixes savedDaily of 50 XP
12days of uptimeyour best streak: 21today: up

Activity

last 24 weeks

Challenges

Real challenges, with real tests.

382 challenges in Python, JavaScript, and SQL. You write your solution in the editor, you run the tests, and they pass or they do not. Behaviour is what gets graded, not the text: if your solution gives the right result, it is right.

All challenges → · All lessons →

  • O(1)
  • O(log n)
  • O(n)
  • O(n log n)
  • O(n²)
  • O(2ⁿ)
pybusqueda_binaria.pyO(log n)
def binary_search(nums, value):
lo, hi = 0, len(nums) - 1
while lo <= hi:
mid = (lo + hi) // 2
if nums[mid] == value:
return mid
if nums[mid] < value:
lo = mid + 1
else:
hi = mid - 1
return -1

Tests

4 / 40.42 s
  • It finds it in the middle
  • Not in the list: -1
  • An empty list
  • Hidden test: A thousand numbers

Career

From Student to Principal.

Your profile climbs the ranks with XP, solved challenges and a technical interview at every step. The same eight names you will meet at work.

  1. 0Estudiante
  2. 100Becario
  3. 300you are hereJunior
  4. 600Semi Senior
  5. 1,000Senior
  6. 1,500Tech Lead
  7. 2,100Staff
  8. 2,800Principal

Technical interview

From Junior on, every promotion is earned by answering questions about code, not by piling up points.

Challenges by difficulty

Semi Senior asks for 10 challenges at O(n) or harder. Senior asks for O(n log n).

A whole course

Tech Lead means finishing every unit of one language, projects included.

Hi! I am Nube. I will be with you all the way to Principal.

Nube shows up when it matters: when you get it right, when you are stuck, while the interpreter is loading and when you have not opened the app in days. Not as decoration in every corner, and never to tell you off.

no livesno punishmentwrong answers come back

Start today

Your first lesson takes five minutes.

Python, JavaScript, and SQL run inside the app, with nothing to install on your computer. No ads inside.

Start in your browser