What you can now do, and what the exam checks

Course 0 was about getting a machine, a language and a habit into working order before anything of value depends on them. Nothing you built here matters. Everything you can now do does.

The part that was never about code

You can ask your computer questions. pwd, ls, cd, a command that fails and an error you read instead of closing. The terminal stopped being a black box in unit 1, and every course after this one talks to you through it.

You have an undo button, and you know which button is not one. A commit is a saved point. A branch is a place to try something without risking what works. git revert takes a change back and keeps the history; git reset --hard throws work away. Knowing the difference is the single fact from this course most worth carrying.

You can read code you did not write. Values, functions, objects, arrays, a decision and a loop — enough to look at a function and say what it does with what it is given. Course 1 hands you code an assistant wrote, and reading it is the whole job.

You have made a real request and read a real answer. A URL, a status code, a JSON body with fields in it. You know why a key inside code the browser receives is a key the visitor has.

You can narrow a failure. Not "change things until it works" — halve the problem, find the smallest case that still breaks, then fix that. Debugging is a method, and you have run it once on purpose.

You can take an assistant's change without taking it on faith. You read a diff, accepted one, committed it with a message that says why. That loop is the rest of the track.

What is still missing

Everything here ran with nothing at stake. You have not yet held a real API key, which is the first thing course 1 gives you and the first thing it can cost you. You have not written a test, so nothing you built checks itself. And you have not built a tool anyone would open twice. Course 1 is all three: a watchlist with your instruments, your notes and live prices, deployed, with the key kept where the browser cannot reach it.

What the exam asks

Ten questions, seventy percent to pass, a twenty-four-hour cooldown before a retake. They are drawn from this course's pool, so a retake is a different paper. Expect:

• Say what it prints. A short snippet — a function, an object, a loop — and the value it produces.
• Read the status. A request came back with a code; say whether the data is there and what to do next.
• Name the destructive one. Two git commands that both "go back"; say which one loses work.
• Find the smallest case. A failure and four things you could try; say which one narrows it.
• Client or server. A piece of code and a question: can the visitor read it?
• Read the diff. Three lines changed; say what the change does before saying whether to accept it.

Nothing depends on the market or on live data. The answers today are the answers next year.

Before you sit it

Each of these is a minute at your desk. Any one that is not names the lesson to reopen first.

• Undo a committed change without losing history, and say which command would have lost it — Git — the undo button for everything you write
• Make one request to /eod/AAPL.US and read the status code and the row count off the answer — Your first request, and the data that comes back
• Take a failing script and cut it to the smallest version that still fails — Narrowing — the smallest thing that still breaks
• Read a three-line diff aloud and say what changed before saying whether it is right — Reading a diff — the skill everything else rests on

Try it now

Run the request from unit 3 once more, from a clean terminal, with the token in an environment variable and nowhere else:

export EODHD_API_TOKEN=...
curl "https://eodhd.com/api/eod/AAPL.US?from=2026-08-24&to=2026-08-28&fmt=json&api_token=$EODHD_API_TOKEN"

What that request answers, fetched with our own key, is below; your terminal should print the same rows.

1. Count the rows and check them against the calendar: 24 to 28 August 2026 is a Monday to a Friday with no US market holiday in it, so the answer is five, and a different count means something worth understanding rather than explaining away.
2. Break it on purpose: misspell the ticker, run it again, and read the status code without looking anything up.
3. Put the working command in a file, commit it with a message that says what it is for, then open the diff of that commit. If you can read all three of those without hesitation, sit the exam.