SDK (software development kit)
Also known as: SDK, software development kit, devkit, dev kit
An SDK, or software development kit, is a bundle of tools, code libraries, documentation, and examples that helps developers build software for a specific platform, device, or service.
Apple's iOS SDK lets developers make iPhone apps, while payment, mapping, or analytics companies provide SDKs that apps use to add their features. While SDKs save developers huge amounts of time, every SDK added to an app brings someone else's code, and sometimes their data collection, along with it.
SDK (software development kit), explained at three levels
At home
An SDK is like a model kit with parts, glue, and instructions. Developers use it to build an app faster instead of making every piece from scratch.
At work
SDKs let developers add payments, maps, or chat to apps quickly, but each one adds third-party code that needs managing.
At home
When an app shares data with advertisers or analytics firms, it's often through SDKs built into it. App privacy labels give hints about these connections.
At work
SDKs typically include libraries, APIs, sample code, and tools. An API defines how to talk to a service, while an SDK provides ready-made code to do so in a given programming language.
At home
Some free apps include many advertising SDKs. In my opinion, paying for an app sometimes buys you less tracking.
At work
Inventory third-party SDKs in apps, review their data collection and permissions, keep them updated for security fixes, track licences, and include them in privacy assessments and software bills of materials.
Real-world examples
At home
Thomas built a small game for his phone. The game engine's SDK handled graphics and sound, so he could focus on designing levels.
At work
Aisha manages a Toronto retail app. An audit found an old analytics SDK sending more data than needed, so her team removed it.
How it compares
| feature | SDK (software development kit) | API (Application Programming Interface) |
|---|---|---|
| What it is | Toolkit with code and tools | Rules for communicating with software |
| Includes | Libraries, docs, samples, tools | Endpoints and documentation |
| Relationship | Often uses APIs | Can be used without an SDK |
| Analogy | Toolbox | Instruction manual |
An API is the doorway. An SDK is the toolkit for using it.
For analysts
In app projects, I'd review every third-party SDK for privacy and security. They often collect data the business never intended to share.
History & origin
Software toolkits existed for decades, but the term SDK became widespread in the 1980s and 1990s, with Microsoft's Windows SDK and Sun's Java Development Kit in 1996. Apple released the iPhone SDK in March 2008, enabling the App Store, and Google released the Android SDK in late 2007. As apps grew, they bundled many third-party SDKs for ads, analytics, and crash reporting, some of which were found collecting location and personal data. Apple introduced privacy manifests for third-party SDKs in 2024, requiring developers to declare what common SDKs collect. In my view, SDKs are the building blocks of modern apps, and each one should be chosen as carefully as a business partner.