You may have heard the term APK and wondered what it meant if you own an Android device. While you can use Android without ever learning what APK stands for, doing so will help you understand and appreciate the platform more.
Let’s define an APK file and why it’s important to Android.
What Is an APK File?
APK is an abbreviation for Android Package (sometimes Android Package Kit or Android Application Package). It is the file format used by Android to distribute and install applications. As a result, an APK contains all of the components required for an app to properly install on your device.
An APK is an archive file, which means it contains multiple files as well as metadata about them. You’ve probably heard of other types of archive files, such as ZIP and RAR.
In general, archive files (such as ZIP) are used to combine multiple files into one, making them more portable or compressing them to save space. When a file archive is used to distribute software, it is referred to as a software package.
Because much of Android is built in Java, APKs are a variant of the JAR (Java Archive) file format. APKs are all ZIP files at their core, but they must contain additional information to function properly as an APK.
So, while all APKs are ZIPs, not all ZIPs are APKs. If you’re curious, you can open an APK file and look inside. Simply open it with a file extraction tool, such as 7-Zip, as you would any other ZIP file. APKs are useless on platforms other than Android unless you install an Android emulator like Bluestacks.
What Are APK Files Used For?
You can install apps on your Android phone using APK files. They’re similar to the APPX files used to install Windows Store apps, as well as the corresponding package files on other platforms. When you open an APK on your device, it contains instructions for installing the app on your phone as well as information about the package itself.
When you go to Google Play to download or update an app, the store will normally install the Google Play Store APK for you. As a result, the Play Store also functions as a package manager—a tool for easily installing, updating, and removing software from a device.
However, due to the open nature of Android, Google Play is not the only place to find and install APKs. It is simple to obtain an APK file from somewhere else, move it to your device, and manually install it. For a comprehensive guide, see How to Sideload Apps on Android.
How Are APK Files Created?
When a developer creates an Android app, they are most likely using Android Studio, the official Android development tool. When the app is ready to ship, Android Studio compiles it and places it all in a single container—an APK.
APKs can have any name they want, but they must have the file extension.apk so that operating systems can understand them. When you download an APK, the filename will usually be something like this:
This is a (shortened) version of Google’s Phone app’s APK name. In the URL of the app’s Google Play page, you can see that the full app name matches the filename:
Because major apps like this are constantly updated, the numbers at the end represent the current version, which can be quite granular.
Why Would I Install APK Files Manually?
Google Play will suffice for the majority of Android installation requirements. However, there are several advantages to manually installing APKs.
One of the most significant is having access to the most recent version of apps ahead of time. When a major Google app (such as Calendar) receives a major update, it may take a week or more for your device to receive the most recent release from Google Play. By installing the APK on your own, you can avoid the wait and update whenever you want.
Sideloading APKs also allows you to install apps that aren’t available on Google Play on your device. You might come across an app that isn’t allowed on Google Play due to a policy violation, or you might want to test your friend’s app that is currently in development.
Downloading APK files from random websites, like desktop software, can be risky. While Google Play has filters in place to detect potentially dangerous apps, there is less protection when installing APKs on your own. They could be malware masquerading as a legitimate app, or they could have been tampered with to include spyware.
What Is Base.APK?
You may have come across a file called base.apk on your phone and wondered what it does. Because these base.apk files are in protected system folders, you’ll only be able to see them if you have root access on your phone.
This is a file that can be found in any app folder. It includes the APK file that you downloaded from Google Play and used to install the app the first time. If you compare the size of this file to the size reported on the app’s Play Store page, they should be the same.
These can be used by APK backup apps to create a copy of the installed apps on your phone. You can also manually copy these files elsewhere for your own use if you prefer.
Now You Know What APK Files Are For
We’ve seen how APKs are the primary format used by Android to distribute and install apps. They are mostly invisible in normal use. However, APKs power all downloads on your phone, so you’re constantly dealing with them, even if you’re not aware of it.
Sideloading APKs from sources other than the Play Store is a useful feature of Android and one of its best features. To avoid exposing your phone to security risks, you should only do so if you trust the origin of the files.
