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 an iOS/Android app. For example, the development of an Android application requires an SDK with Java, for iOS apps an iOS SDK with Swift, and for MS Windows the .NET Framework SDK with .NET. There are also SDKs that are installed in apps to provide analytics and data about activity. Prominent examples include Google, InMobi and Facebook.
It may be something as simple as the implementation of one or more application programming interfaces (APIs) in the form of some libraries to interface to a particular programming language or to include sophisticated hardware 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 also frequently include sample code and supporting technical notes or other supporting documentation to help clarify points made by the primary reference material.
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SDKs may have attached licenses that make them unsuitable for building software intended to be developed under an incompatible license. For example, a proprietary SDK will probably be incompatible with free software development, while a GPL-licensed SDK could be incompatible with proprietary software development. LGPL SDKs are typically safe for proprietary development.
The average Android mobile app implements 15.6 SDKs, with gaming apps implementing an average of 17.5 SDKs. The most popular SDK categories for Android mobile apps are analytics and advertising.
SDKs may be unsafe (as SDKs are implemented within apps, but are running an independent code). Malicious SDKs (with honest intentions or not) may violate users’ data privacy, damage the apps’ performance or even get apps banned from Google Play or iTunes. New technologies allow app developers to control and monitor SDKs in real time.
A software engineer typically receives the SDK from the target system developer. Often the SDK can be downloaded directly via the Internet or via SDKs marketplaces. Many SDKs are provided for free to encourage developers to use the system or language. Sometimes this is used as a marketing tool. Freely offered SDKs may still be able to monetize, based on user data taken from the apps, which may serve the interests of big players in the ecosystem, for example the operating system.
A SDK for an operating system add-on (for instance, QuickTime for classic Mac OS) may include the add-on software itself to be used for development purposes, albeit not necessarily for redistribution together with the developed product. Between platforms where it is possible to develop applications that can at least start up on a system configuration without the add-on installed, and use a Gestalt-style run-time environment query to determine whether the add-on is present, and ones where the application will simply fail to start, it is possible to build a single binary that will run on configurations with and without the add-on present, albeit operating with reduced functionality in the latter situation.
Providers of SDKs for specific systems or subsystems may sometimes substitute a more specific term instead of software. For instance, both Microsoft and Apple provide driver development kits (DDK) for developing device drivers.