The Understanding Engine
It won't give you the answer.
Every other AI tool optimises for producing correct code. CodeTutor optimises for making you able to write it without one. It builds a working model of how you learn, generates your next step from what you just did, and escalates through five hint levels — none of which is something you could paste.
Passkey sign-in. No card, no trial timer.
Tutor · live example
No hint given
Ask it anything about the exercise you are stuck on.
Including the thing you are about to ask.
A scripted example of real tutor behaviour. Nothing here calls a model.
The difference
Two ways to answer the same question
One of these leaves you with code. The other leaves you able to write it. Drag the handle and decide which one you actually want at 11pm the night before it is due.
Any other assistant
How do I get the second largest number in a list?
def second_largest(nums):
if len(nums) < 2:
return None
best = second = None
for n in nums:
# … and so onCorrect, complete, and pasteable. You have the answer. Tomorrow you will not have the skill.
CodeTutor
How do I get the second largest number in a list?
You have already written the one-largest version of this, and it worked. So: walk the list once, holding the best you have seen. Now hold a second thing.
When a number is big enough to take first place, where does the number that used to be in first place go?
A question, not a solution. You write it. Tomorrow you can write it again.
Drag the handle, or focus it and use the arrow keys.
How a path is built
Nothing is decided in advance
Not a week's plan, not the next three lessons, not even the next two steps. Each one is chosen when you ask for it, from everything that has happened up to that second.
Press it and watch what happens to the step after the exercise.
Goal
You say what you want to be able to build
A language, a thing you want to make, how you like to learn, and how much time you actually have. Not a syllabus — a destination.
Placement check
A short check with no pass mark
It exists to seed the model, so the first real step starts where you are rather than where a course assumes everyone is.
Explanation
Why a list keeps its order
Written for you, using the example you said you cared about — and it ends by telling you when not to reach for a list at all.
Exercise
Reverse a list without the built-in
You get stuck around the middle index. You ask for a hint. You get a question back.
Review
Six dimensions, of which correctness is one
It also judges, separately, whether you appear to understand the code you just wrote. Working code arrived at by guessing scores high on the first and low on the second.
Task
The objective, restated word for word
The brief is the goal you set at the top. If you can do it, the objective is met. That is the whole test.
The Understanding Engine
A working model of what you can do
Every concept in the taxonomy, with your standing on it and how much that estimate is trusted. Mastery moves on evidence, decays if you leave it, and never moves because you said so.
Concepts
Select one to light it and everything it stands on.
Nothing selected. Every concept in the taxonomy is here, including the ones this learner has never touched — an untouched concept is information, not a gap in the picture.
Code review
Correctness is one of six things it looks at
And whether you understand what you wrote is judged separately from all six — because code that works and code you could write again are not the same achievement.
One submission, six scores
Achievements
Nothing rewards showing up
No badge for logging in, opening a lesson, or accumulating hours. The locked ones are shown too — what a platform refuses to celebrate says more than what it does.
For schools
Built for a classroom, not retrofitted to one
A teacher's view of where a class is actually stuck, single sign-on per school, and a model each learner can read and argue with.
Teachers see where the class is stuck
Not who logged in. Which concept the room is failing on, which learners are guessing their way to correct answers, and which are quietly ahead.
Single sign-on, per school
Each school gets its own organisation and its own identity provider. Accounts are created on first sign-in; there is nothing to import and nothing to sync.
The learner owns the model
Every inference the platform holds about a learner is readable by that learner, in plain language, and any of it can be dismissed permanently.
Questions
The obvious objections
Will it ever just tell me the answer?
No. Hints escalate through five levels and stop. Level five is a worked approach in prose — the shape of the solution, described — and there is no sixth level. If you want the answer pasted, every other tool will do that for you.
How is this different from asking a chatbot?
A chatbot answers the question you asked. This decides what you should be doing next, from a model of what you can actually do — built from your submissions, your hints, and your mistakes rather than from what you say your level is.
What does it actually know about me?
Per-concept estimates of what you can do, with a confidence attached, plus short typed claims about how you learn. You can read all of it, and dismiss any of it permanently.
Do I need to know anything to start?
No. The placement check has no pass mark; it exists to seed the model so that the first step starts where you are. If it turns out you already know something, you skip straight past it.
Which languages does it teach?
You choose one when you set your goal, and the curriculum is generated for it. The teaching is about judgement — when not to use the thing you just learned — which is the part that transfers.
Is this page collecting anything?
No. It is a static file with no analytics, no cookies, no forms and no requests to anywhere. The buttons are links to the platform's sign-in, and nothing happens until you follow one.
Learn it so you keep it.
Set a goal, take a five-minute check with no pass mark, and get your first step. Not a syllabus — a step, chosen for you, once it knows something true about you.
Passkey sign-in. No card, no trial timer.