What is the difference between an SDK and an API?

An API is the interface a service exposes over the network. An SDK is a ready-made library that calls that API for you and adds device-side features such as token registration, offline queues and message rendering. Many vendors offer both: the SDK in the app and the API for your backend.

Do SDKs slow down apps?

Each SDK adds some size and startup work. Well-built SDKs initialize quickly and send data in the background, but stacking many analytics and marketing SDKs adds up. Audit them periodically and remove ones you no longer use.

Which mobile SDKs do I need for push and in-app messaging?

One engagement SDK usually covers push registration, in-app messages and event tracking. Compare options for your framework in our guides to push services for React Native and Flutter.

Back to Glossary

Mobile & Push

Mobile SDK(Mobile Software Development Kit)

A library a vendor provides for iOS, Android or cross-platform frameworks so an app can use its service, such as push notifications, analytics, payments or in-app messaging, without building it from scratch.

Definition

A mobile SDK (software development kit) is a package of code, usually a library plus documentation and sample apps, that developers add to an iOS or Android app to connect it to an external service. Marketing and engagement SDKs register push tokens, identify users, track events and screens, display in-app messages and report results back to the vendor. SDKs come as native libraries (Swift for iOS, Kotlin for Android) and as wrappers for cross-platform frameworks such as React Native, Flutter and Expo.

Why It Matters

For marketers, the SDK is what makes mobile channels possible: without it there are no push tokens, no in-app messages and no behavioral events to trigger journeys from. For developers, every SDK adds app size, startup work, privacy disclosures and maintenance with each OS release. Choosing vendors with well-maintained, lightweight SDKs that cover your app's framework saves months of work and avoids App Store review problems.

How It Works

A developer installs the SDK with the platform's package manager, such as Swift Package Manager or Gradle, or npm and pub for cross-platform apps. The app initializes it at launch with an API key, then calls methods such as identify when a user signs in, track for events and a push registration call for tokens. The SDK queues data, sends it to the vendor in batches, and listens for instructions like in-app messages to show. When users sign out, a reset call unlinks the device. Updates follow new OS versions, so apps upgrade SDKs regularly.

Example

Typical calls an app makes to a messaging SDK:

Sequenzy.configure(publicKey: "seq_pk_...", companyId: "your-company-id",
                   identityTokenProvider: { email in try await MyBackend.sequenzyToken(for: email) })
Sequenzy.identify(email: user.email)
Sequenzy.track("workout_completed", properties: ["minutes": 30])
let status = await Sequenzy.requestPushPermission()

From these calls the platform knows who the user is, what they did and how to reach them.

Best Practices

1Check that the vendor supports every framework your app uses, including React Native, Flutter or Expo
2Initialize SDKs lazily where possible to protect app startup time
3Identify users only after sign-in and reset on sign-out to avoid mixing profiles
4Keep your privacy manifest and store disclosures in sync with what each SDK collects
5Pin SDK versions and upgrade deliberately, testing push and in-app flows each time

SDKs for iOS, Android, React Native and Flutter

Sequenzy's mobile SDKs register push tokens, track events, show in-app messages and report geofences, all feeding the same sequences as your email.

Learn More

Mobile SDK Platforms

Platform	Language	Package manager
iOS	Swift	Swift Package Manager
Android	Kotlin	Gradle
React Native and Expo	TypeScript	npm
Flutter	Dart	pub