A software development kit (SDK or devkit) is typically a set of software development tools that allows the creation of applications for a certain software package, software framework, hardware platform, computer system, video game console, operating system, or similar development platform. To enrich applications with advanced functionalities, advertisements, push notifications, and more, most app developers implement specific software development kits. Some SDKs are critical for developing a platform-specific app. For example, the development of an Android app on Java platform requires a Java Development Kit, for iOS apps the iOS SDK, and for Universal Windows Platform the .NET Framework SDK. There are also SDKs that are installed in apps to provide analytics and data about application activity; prominent creators of these types of SDKs include Google, InMobi, and Facebook.
An SDK can take the form of a simple implementation of one or more application programming interfaces (APIs) in the form of on-device libraries to interface to a particular programming language, or it may be as complex as hardware-specific tools that can communicate with a particular embedded system. Common tools include debugging facilities and other utilities, often presented in an integrated development environment (IDE). SDKs may also include sample code and technical notes or other supporting documentation such as tutorials to help clarify points made by the primary reference material.
SDKs often include licenses that make them unsuitable for building software intended to be developed under an incompatible license. For example, a proprietary SDK is generally incompatible with free software development, while a GPL-licensed SDK could be incompatible with proprietary software development, all particularly for legal reasons. However, SDKs built under the GNU Lesser General Public License (LGPL) are typically safe for proprietary development.
The average Android mobile app implements 15.6 separate SDKs, with gaming apps implementing on average 17.5 different SDKs. The most popular SDK categories for Android mobile apps are analytics and advertising.
SDKs can be unsafe (because they are implemented within apps, but yet run separate code). Malicious SDKs (with honest intentions or not) can violate users' data privacy, damage app performance, or even cause apps to be banned from Google Play or the App Store. New technologies allow app developers to control and monitor client SDKs in real time.
Providers of SDKs for specific systems or subsystems sometimes substitute a more specific term instead of software. For instance, both Microsoft and Citrix provide a driver development kit (DDK) for developing device drivers.