adb.exe not found after installing Android Studio

May be adb.exe file is missing form your computer. Try deleting platform-tools folder and re-download it from SDKManager.

Mac OS El Capitan has it located at /Users/[username]/depot_tools/src/chrome/browser/devtools/device

The adb.exe file will be located at your Android SDK folder, inside platform-tools

...\android-sdk-path\platform-tools\adb.exe

The default location where Android SDK is installed is:

C:\Users\<insert username here>\AppData\Local\Android\sdk\

So adb will be located at:

C:\Users\<insert username here>\AppData\Local\Android\sdk\platform-tools\adb.exe

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To access it on a command line, open cmd.exe and type:

cd C:\Users\<insert username here>\AppData\Local\Android\sdk\platform-tools\

and then your normal command

adb <insert parameters here>

In my case, adb.exe got deleted after Android Studio update. I copied all the contents under platform-tools to another directory, deleted all the contents under platform-tools and installed platform-tools from Android SDK Manager.