How an exercise works here

If you have used other training sites, the first thing you will notice is that there is no quiz after every paragraph. We tried that. It produces people who can answer "which cookie flag blocks JavaScript?" but freeze in front of a real login form.

So every exercise here has the same three parts.

1. The course

A short written lesson that explains one idea properly, in plain language, with code and diagrams. It assumes nothing you have not been told in a prerequisite exercise, and it says what those prerequisites are at the top. Read it slowly. It is deliberately not long.

2. The lab

Then you do the thing. Depending on the exercise that means reading a snippet of real-looking code and finding the dangerous line, tracing a request through a log, or working a problem on your own machine. The lab is where the idea turns into a skill.

3. The key

Finally you submit a key — a specific answer you can only get by doing the lab. Keys are not case-sensitive, and each one is worth points the first time you get it right. Points feed the leaderboard and your rank; they are a nudge, not the point.

Hints and solutions

Every key has a hint that you can open freely. A hint points you at where to look; it never gives the answer. If you want the answer explained, each key also has a written solution. Solutions are included with Pro, and they also unlock for anyone the moment they solve that key — so you can always check your reasoning against ours afterwards.

Badges and tracks

Exercises are grouped into badges: ordered sets on one skill, like Injection or Code Review. Finish every exercise in a badge and it is awarded automatically, together with a certificate at a public link you can put on a CV. Tracks are longer curricula of chapters for people who want to be told what to do next.

A note on the old rooms

If you were here before the rebuild: your points, streaks, passes and payments are exactly as they were. Rooms you had finished that have a new version are marked complete in the new catalogue. The rest of the old material is being rewritten into this format a batch at a time.

Start with How HTTP Works — it is free, it takes twenty-five minutes, and everything else builds on it.