Try an assignment

The fastest way to understand this tool is to be a student for five minutes. There is a real assignment attached to this page. Press Assignment in the header, or Open assignment on the card at the bottom, and it slides up in a drawer along the bottom of the window — its own notebook, running in your browser, while this page stays readable above it.

Nothing is installed and nothing is sent anywhere. The first open takes a few seconds while the browser fetches Python.

What to do

1. Read Q1 and write the function. keep_between(values, lo, hi) should return the values from lo to hi, bounds included. Replace the # YOUR CODE HERE line and delete the pass.
2. Watch the check below it. Before you answer it says Complete the function above first — that is the check waiting, not an error. Once the function returns a list the check runs and tells you which conditions pass. Get one wrong on purpose and read what it says.
3. Do Q2. It asks for a value rather than a function, so its answer cell starts as mean_rt = .... That ... is what a stripped solution leaves behind.
4. Read Q3. It is a written question, so it has a text box and no check. A person reads that one.

The drawer is drag-resizable, Minimize tucks it down to its bar without stopping the notebook, and your answers save into this browser as you type — close the tab and they are still there tomorrow.

What is real here, and what is missing

Everything you interact with is the real thing: this is a student notebook in the shape grader publish produces, and Check is the same g.check(...) call a student runs in a course, rendering the same callouts and the same per-condition marks.

Three controls are missing, because a documentation page has no grading server behind it:

In a course	What it does	Why it is not here
g.signin_button()	starts the sign-in handshake, once per notebook	there is no server to sign in to
g.submit_button("demo-q01")	records an attempt for that question	nothing to record it against
g.feedback("demo-q01")	shows the score and the instructor's comments	no attempt, no feedback

In a real assignment those sit at the top and after each question, and the page looks like this:

There is also a fourth thing you cannot see, and that one is deliberate even in a course: each check cell here ends with a # HIDDEN TESTS comment. In the instructor's copy that comment is a stricter condition, removed when the student copy was generated and put back at grading time. It is why a question that passes Check can still lose a point — and why the feedback tells you which condition failed.

Then read the other side

What the instructor wrote puts the instructor's notebook and this student copy side by side, so you can see exactly what publishing removed.

If you want the full student path instead — MoLab, a cluster, a laptop, signing in, attempts, feedback — start at Open an assignment.

Running the demo yourself

The two notebooks are ordinary files in the repository. With uv installed:

# the student copy, the one in the drawer above
uv run marimo edit --sandbox \
  https://raw.githubusercontent.com/ljchang/marimo-grader/main/docs/content/demo/assignment.py

# the instructor copy, with solutions and hidden tests
uv run marimo edit --sandbox \
  https://raw.githubusercontent.com/ljchang/marimo-grader/main/docs/examples/reaction-times.py

--sandbox reads the dependency list inside the notebook and builds an environment for it, so it runs the same way it does in the drawer.

Assignment: Demo assignment: reaction times

1. Q1. Keep the plausible trials
2. Q2. The average of what is left
3. Q3. What the trimming costs

Open assignment Opens in a drawer at the bottom of the page, so you can keep reading while you work. Autosaves in this browser.