Is it safe to delete the AppData folder?

No, never delete the AppData folder itself. It's where your apps keep their settings, profiles, caches and sometimes data that exists nowhere else. Deleting it would reset or break most of your apps. Some folders inside it are perfectly safe to remove, though, and they're often where the space is.

Quick verdict:

AppData, Local, LocalLow, Roaming themselves: never delete.
Folders of apps you've already uninstalled: usually safe.
Caches (folders called Cache, Code Cache, GPUCache, CrashDumps) and Local\Temp: usually safe while the app is closed.
Settings, profiles, Local\Programs, Local\Packages, browser User Data: leave them, or clean them from the app itself.

What is the AppData folder?

Each Windows user has one, at C:\Users\<your name>\AppData. It's hidden by default, so the easiest way in is to type %AppData% or %LocalAppData% into the File Explorer address bar. Inside there are three folders, defined in Microsoft's Known Folders list:

Folder	Shortcut	What goes there
`AppData\Local`	`%LocalAppData%`	Data that stays on this PC: caches, per-user installs, Store app data, your Temp folder. Usually the biggest.
`AppData\LocalLow`	none	Data for apps running with restricted ("low integrity") permissions, such as sandboxed browser parts and many games built with Unity.
`AppData\Roaming`	`%AppData%`	Settings and profiles meant to follow you. On company networks with roaming profiles they're copied to other PCs you sign in to.

Apps decide for themselves what to put where, and few of them clean up after themselves. That's why AppData grows: caches get bigger, updates leave old versions behind, and uninstallers often leave the app's folders in place.

How much space does it use?

Settings → System → Storage doesn't list AppData as a category of its own. To get a number, right-click the AppData folder and choose Properties. It can take a while to count.

A disk space analyzer shows you which folders are big, which is what you actually need. With SquirrelDisk, which is free:

On the home screen, click A folder and paste %LocalAppData% into the folder dialog. Do the same for %AppData%. From a terminal: squirreldisk %LocalAppData%.
The chart builds while scanning, with the biggest folders listed first. Click one to see inside, for example a browser's cache or a launcher's download folder.
For a quick text summary without a window, run squirreldisk scan %LocalAppData% --depth 2 --top 5.

SquirrelDisk won't let you delete AppData, Local, LocalLow or Roaming themselves, and it asks for an extra confirmation before deleting anything inside them. It runs as your normal user, so it sees your AppData fully.

How to delete it safely

Start with the built-in tools

Settings → System → Storage → Temporary files clears your Local\Temp folder and other Windows leftovers. See Is it safe to delete temp files?
Settings → Apps → Installed apps: uninstall apps you don't use. That's the cleanest way to remove their AppData folders, although some leave a few behind.
Clear caches from inside the app. Browsers, Teams, Spotify and many launchers have a "clear cache" option. It's safer than deleting folders, because the app knows which files are only cache.

Then clean by hand

Close the app whose folder you're cleaning, including from the system tray. Check Task Manager if you're unsure.
Delete the folders of uninstalled apps. If you uninstalled an app months ago and its folder is still in Local or Roaming, it's safe to remove. When the name doesn't tell you which app it belongs to, search for it before deleting.
Delete cache folders of apps you still use. Look for folders named Cache, Code Cache, GPUCache, ShaderCache or CrashDumps inside the app's folder. The app rebuilds them, and may start a little slower the first time.
Use the Recycle Bin, not Shift + Delete, and empty it only after using the apps for a few days. If something misbehaves, restore the folder.

What you should not delete

Inside AppData	Safe to delete?	Why
`Local\Programs`	No	Apps installed just for you, such as Visual Studio Code. Uninstall them from Settings.
`Local\Packages`	No, not by hand	Microsoft Store app data. See AppData\Local\Packages.
`Local\Microsoft` and `Roaming\Microsoft`	Mostly no	Windows and Office settings, credentials, Start menu, Outlook data.
Browser `User Data` or `Profiles`	No	Bookmarks, passwords, history and extensions. Clear the cache from the browser instead.
An app's main `Roaming` folder	Only if uninstalled	Settings, profiles, and for some apps local mail or saved games.
`Local\Temp` contents	Yes	Skip files in use.
Cache folders	Yes, app closed	Rebuilt automatically.

Be careful with anything that might hold data only on this PC: local email stores (some mail apps keep messages under AppData), notes apps, password managers that store a local vault, and game saves that don't sync to the cloud. If in doubt, back the folder up first, or leave it.

If you've already deleted something important, restore it from the Recycle Bin. If it's gone, reinstall the app: it will recreate its folders with default settings, but personal data that was only there is lost unless you have a backup.

Better ways to free space

AppData is rarely worth more than a few gigabytes of careful cleaning, and the risk grows the deeper you go. Before you spend an hour in it, check the bigger, easier wins: Windows.old after an upgrade, your Downloads folder, and apps or games you no longer use. A full scan of drive C: with SquirrelDisk shows you all of these at a glance, so you can start with whatever is largest.