5 Whys tool
Chain the 5 questions down to the root cause and note the corrective action. It is saved in your browser.
Your progress is saved automatically in this browser (it is not sent to any server).
How it works
It does not calculate anything: it organizes the reasoning. You write the problem, answer "why?" five times (each answer is the basis of the next question), note the root cause you reached and the corrective action.
Five is a guide, not a fixed rule: the root cause may appear sooner or later. What matters is to keep asking until the next answer no longer adds new information, and that every link can be verified with facts rather than assumptions.
What you write is saved in your browser (nothing is sent to any server), so you can close the page and pick it up later. For problems with several possible causes, it is best to combine it with an Ishikawa diagram.
Sources
These are the ones from the article where the theory behind this tool is developed.
Where does the technique come from, and is there a real applied case? It is in the article 5 Whys: reaching the root cause by asking why, 5 times.