Logging that helps you at 3am
By the end of today you can write log lines that answer questions during an incident, choose levels deliberately, and explain why structured logs and a correlation ID change what is possible.
YesterdayOn Day 7 you debugged with a reproduction and a debugger. Neither is available when it is happening in production to somebody else.
TomorrowTomorrow, containers, so the environment your logs come from is one you can reproduce.
Why this matters
During an outage you cannot add logging. Whatever you wrote months ago is all you have, and most people discover then that they logged the wrong things.
- Log levels
- Structured logging
- Correlation IDs
- What never to log
Learn it
75 minCopy this into Claude or ChatGPT. It quizzes you before it explains anything, which is deliberate. The resources under it are how you check what it told you.
Today's Master Prompt
Free · sign inA prompt written for this day alone: your level, the exact scope, what to leave out, and an instruction to quiz you before it explains anything. Paste it into Claude or ChatGPT and it teaches you today's material.
Check it against something that is not a model
An assistant can be fluent and wrong, and on a topic you met today you will not catch it. These cover the same ground and were made by people who do this for a living, so they are what you hold the explanation up against. They are other people's work and we only link to them, so judge them for yourself.
3 hand-picked resources
Free · sign inVideos, official docs and articles covering the same ground, each opened and annotated by hand. They are what you check the assistant against on a day you cannot yet catch it being wrong.
Build it
45 minAdd structured logging to one endpoint: log the request start with a generated correlation ID, every external call with its outcome and duration, the decision taken with the values behind it, and the response status. Then make it fail and check whether the logs alone tell you why, without reading the code.
Recall it
20 minAnswer out loud, reveal, then mark honestly whether you had it. That score is the only thing on this page you do not get to choose.
5 recall questions
Free · sign inQuestions you answer from memory, then grade yourself against the real answer. The score is carried into the mastery rating below it, so an honest miss cannot quietly become a tick.
Rate it
Completion and mastery are tracked separately. Be honest, because an inflated rating only means the concept resurfaces sooner.
Mastery tracking
Free · sign inRate yourself against five named criteria per concept. Completion and mastery are tracked separately, and anything you rate shakily comes back automatically on a spaced schedule.
Recap
- 01Logging exists for the failure you cannot reproduce or attach to
- 02A useful line names what happened and the values behind it
- 03A correlation ID is what makes interleaved logs readable
- 04Never log a secret; logs travel further than your database
Your progress
Free · sign inMark days complete, pick up where you left off across devices, and watch completion and mastery diverge. Free, and the account exists only so ninety days of work cannot vanish with a cleared browser.