Funded by the teams who pay

The Free Stuff.

No credit card, no trial clock, no account to start.

01The daily
Today's question
One sharp engineering question a day, graded with the why. A new one tomorrow.
Open today's
02The challenges
Hosted games
Live game modes for a room full of engineers. You host, everyone you invite plays free.
Host a game
03The courses
Levels 1 and 2, every course
Structured courses taught in thirty-second reps. The first two levels of all of them.
Start a course
04Slack
A question in your channel
The bot posts one question a day to one channel you pick. No seats, no trial.
Add to Slack, free
05The letter
The Retrieval
Our biweekly letter on evidence and practice. Everyone starts at issue one.
Subscribe
06The coding agent
A rep inside Claude Code
One short question about the thing you just built, inside the coding agent you already run. Answer with one letter or ignore it.
Connect your agent
07The research
The research publication
Long-form essays on what passive AI use does to understanding. Every claim graded and sourced.
Read the research

01 · Try one right now

Answer one question.

A rep is one question, answered and graded, with the reason underneath. It takes thirty seconds, and it is the unit everything on the shelf above is counted in.

+ 11 tracks

General · HTTP · about 30 seconds

What makes an HTTP method “safe”?

Pick one. A wrong guess still makes the answer stick.

[02]Why the habit worksThirty seconds, once a day

Answering beats reading. That is the whole trick.

Pulling an answer out of your own head is what fixes it there. Reading the same thing again feels productive and mostly is not. The difference is small on Monday and enormous by the following year, because every time the answer comes back to you the next slide downhill gets slower and the level it settles at gets higher.

Model · illustrativeFig. 01 · what one question a day is wortha model, not a measurement

A model, not a measurement: the curve shapes are illustrative, and they are the same shapes the cognitive-debt figure uses on the research page, so the two can never disagree. The pinned anchors are measured. Roediger & Karpicke 2006 (N=180): re-reading a passage four times gave 83% recall after five minutes and 40% after a week, while testing yourself gave 71% then 61%. Adesope et al. 2017: retrieval beats re-reading, g = 0.51 across 272 comparisons. Pan & Rickard 2018 (N=10,382): the gain still shows on problems you have never seen. All of it, graded and sourced.

The part worth sitting with: the group that re-read four times was the most confident they would still remember it a week later. They were the group that remembered least. Feeling fluent and being able to recall are different things, and only one of them shows up when production breaks at two in the morning.

The rest of the evidence

Every claim we make, graded and sourced, with the caveats next to the claims they belong to. Free, like this page.

Read the research

[03]Pass it onOne link, no account

Send someone a question, not a pitch.

The engineer who taught you something was not selling anything. Do the same: send one question to the person on your team who would argue about the answer.

01
Send them today's question
It opens as a question, not a landing page. No wall in front of it.
Open today's
02
Drop it in your team channel
Or install the bot and let it post one every morning, free, one channel.
Add to Slack, free

[04]If you want the restOnly when it has earned it

Free is not the demo. It is the base.

Pro opens the rest of every course. Team puts the habit in front of everyone you work with. Those two pay for the research behind the questions, for keeping them current, and for the shelf above. Prices are on the pricing page, in full, with no call required.

See Pro and Team, with prices