Open File Explorer. Right-click any file. Count the menu items you actually use.
Now count the ones you don't recognize.
That second number is usually 10 to 30 — and it's the visible tip of a much larger customization system that Windows keeps out of Settings entirely. There's no Settings page for what's in your right-click menu. None for which app owns your file thumbnails. None that lists File Explorer's sidebar entries. The system is real, it's powerful, and it's almost completely invisible.
After years of digging through it, I've found it breaks down into 5 layers.
The 5 layers
When you install a Windows app, it can wire itself into your shell across up to five layers — and most apps touch three or four of them without ever telling you:
Right-click verbs — the entries that appear when you right-click a file, folder, drive, or empty space. Each surface is separate, which is why the same app can show up in one menu and not another.
File-type behaviors — thumbnails, the preview pane, the metadata columns in Details view, and whether Search can look inside a file. All per-extension, all owned by whichever app claimed them last.
Sidebar / namespace entries — the items in File Explorer's left rail (OneDrive, This PC, Network, the "Linux" entry WSL adds). Each is a registered extension, not a folder.
Dispatchers — the routing tables Windows checks when something happens: what opens a mailto: link, which apps appear under "Open With", what fires when you insert a USB stick.
Suppressors — the hidden layer that can hide any of the above even when it's correctly installed. This is the one almost nobody knows exists.
Settings exposes maybe 5% of layer 1 and essentially nothing from layers 2 through 5.
Layer 1 — the right-click menu is a merge, not a list
The menu you see isn't stored in one place. Windows builds it on the fly by merging entries from many separate surfaces — all-files, folders, the empty space inside a folder, drives, and per-file-type rules — and then layers per-user overrides on top of machine-wide ones. Windows 11 added a second, newer kind of entry on top of that (the reason "Show more options" exists at all).
The practical upshot: an entry you want gone can be defined in a place you'd never think to look, and a per-user rule can quietly override a system one.
Layer 2 — why one file type loses its thumbnails
Ever had thumbnails break for exactly one format — HEIC, RAW, DWG — while everything else is fine? That's this layer. Each file type points at the app responsible for its thumbnail, its preview, its indexing. When an app is removed but its claim isn't, the pointer dangles and the thumbnail dies. There's no Settings screen that tells you which app owns .heic previews versus .raw.
Layer 3 — the sidebar is extensions, not folders
Every item in Explorer's left rail is a registered namespace extension, not a real folder. That's why you can't just "delete" OneDrive from the sidebar the way you'd delete a folder — and why removing it cleanly is a documented hassle Microsoft handles through group policy rather than a simple button.
Layer 4 — the menus full of dead apps
Open your "Open With" menu. Odds are it lists apps you uninstalled long ago. That's because Windows assembles that list from several independent sources, and most uninstallers clean only one of them. The same pattern explains AutoPlay popups for hardware you no longer own, and default-app handlers that point nowhere.
Layer 5 — the hidden hand
This is the surprising one. An entry can be correctly installed in layers 1–3 and still not appear, because a separate suppression layer can hide it shell-wide. So "I removed OneDrive from File Explorer" can mean five different things depending on which layer actually did the work — and if two layers disagree, you get the classic "I deleted it but it's still there" (or the reverse).
The 15-overlay cap nobody warns you about
One concrete favorite. Those little badges on icons — the OneDrive green check, Dropbox's arrows, Git status marks — are "icon overlay" handlers, and Windows hard-caps the number it will display at 15. They're loaded in alphabetical order, and anything past the 15th is silently dropped.
Install OneDrive, Dropbox, Box, and Google Drive and they eat most of the slots. Git's badges sort later in the alphabet, fall off the end, and vanish — with no error, no warning, nothing. The popular "rename your handlers with leading spaces so they sort first" trick works only until the next update rewrites the entries. The real fix is to turn off the overlays you don't use so the cap stops mattering.
Why a 5-year-old Windows install is full of junk
Each app wires into several of these layers on install. On uninstall, it deletes its program files and a key or two — but leaves the shell wiring behind, because that wiring was added by a different mechanism than the uninstaller knows about. Multiply by every app you've ever installed and a mature Windows install is carrying hundreds of dead shell entries pointing at files that no longer exist. They don't crash anything — Windows just skips the broken ones — but they slow Explorer down and clutter every menu.
The tool
You can see all of this yourself if you know every place to look — but the places aren't documented in one spot, and there's no Microsoft tool that shows the whole picture at once.
So I built one. Kontext scans more than 40 shell-component locations across all three registry hives at once and lays them out in one searchable list — with icons and, for the apps it recognizes, real names instead of raw identifiers, so you can finally tell what each entry actually is. Flip anything off with a checkbox; every change is backed up the instant before it's applied, and one click restores it exactly as it was — including bringing back entries you turned off earlier.
Disclosure: I'm the author. It's code-signed, runs on Windows 10/11 (x64), and has a free trial. https://amathlai.com/kontext.html
It isn't the only context-menu editor out there — ShellExView, ContextMenuManager and others exist — but as far as I've found, it's the only one that covers all five layers instead of just the right-click subset.
TL;DR
Windows shell customization is a 5-layer system, and Settings shows about 5% of it.
The right-click menu is merged live from many sources — that's why entries hide in unexpected places.
Icon overlays silently cap at 15; extra ones just disappear.
A hidden suppression layer can override everything else.
Uninstallers leave most of their shell wiring behind, which is why old Windows installs feel cluttered.