A tier list ranks things into bands labelled S, A, B, C, D and F. The letters are a school grading scale, except for the first one, which is not.
Where S came from
S sits above A and stands for shu — 秀, "excellence" — or in some tellings simply "special". It arrived through Japanese games: arcade titles and later gacha games used a rank above the top of a conventional scale for the rarest items and strongest characters.
Fighting game communities picked it up for character rankings, and from there it spread to ranking anything at all. The oddity of a scale that runs S, A, B, C, D, F is entirely explained by S having been added to a scale that was already complete.
The missing E is inherited too: American school grading skips it, on the reasoning that E for "excellent" and E for "failing" would be confused. F stands for fail.
Why good tier lists avoid drag and drop
HTML has a native drag-and-drop API. It does not fire on touch devices at all.
That is not a minor gap. Tier lists are made on phones more than on desktops, so a tier list built on native drag and drop simply does not work for most of the people trying to use it — and it fails silently, with items that will not move and no explanation.
The workaround is reimplementing dragging with pointer events, which works but is fiddly, and remains unusable with a keyboard. Tap-to-select then tap-to-place works on every device, is keyboard-reachable, and is faster once you have done it twice.
Why the image is drawn rather than screenshotted
There is no browser API that converts an element into an image. The usual workaround wraps the HTML in an SVG foreignObject and rasterises that, which works in some browsers and is blocked outright by a strict content security policy.
Drawing the board directly onto a canvas avoids all of it and has a genuine advantage: the output is a fixed size regardless of your window width, zoom level or font settings. A screenshot varies with all three.
Questions people ask
Is there a standard set of tiers? S to F is the common one. Some use S+ and SS above it, which is the same escalation happening again.
How many items per tier? However many belong there. A list where every tier has the same count is usually one where the ranking was avoided.
Does the order within a tier mean anything? By convention no — that is what having tiers is for. Some people rank within tiers anyway.
Why F and not E? American school grading skips E to avoid confusion with "excellent". F is fail.
The tier list maker uses tap-to-place so it works on a phone, and the spin the wheel and random team generator cover the other ways of sorting a list of things.