Mobile Engineer
Castle
WorldwideremotePosted 29 days ago
Skill Required
Mobile-EngineeringSDK-DevelopmentiOS-DevelopmentAndroid-DevelopmentMobile-SecurityMobile-EngineerMobile-Device-EngineerMobile-Solutions-EngineerMobile-Android-EngineerStaff-Mobile-EngineerFreelance-Mobile-EngineerMobile-Test-EngineerMobile-Engineering-ManagerJunior-Mobile-EngineerCD pipelinesEngineeringJavaScriptdesigninganalyticssecuritybuildingAndroidKotlindesignC++SwiftCI/CDRustAPIsiOSandCICDFulltime
Key highlights
- US‑level salaries globally
- Remote‑friendly in Europe
- Requires experience with Kotlin and Swift
- Must have worked on mobile SDKs or similar infrastructure
- Strong understanding of mobile dependency management, build systems, and release workflows
- Experience with Gradle, CocoaPods, Swift Package Manager, or similar tooling
Role overview
Responsibilities
- Own the mobile SDKs end to end
- Work on the Kotlin and Swift codebases, evolving the SDK architecture
- Design APIs used by thousands of developers
- Ensure mobile instrumentation remains reliable as the mobile ecosystem evolves
- Design and improve the architecture of iOS and Android SDKs
- Build reliable signal collection mechanisms across device models and OS versions
- Maintain SDK performance and minimize overhead inside customer applications
- Design APIs and developer experience for third‑party integrations
- Manage build systems, versioning, CI/CD pipelines, and artifact publishing
Requirements
- Must have already worked on mobile SDKs or similar infrastructure that runs inside other applications
- Strong experience with Kotlin and Swift
- Understand mobile dependency management, build systems, and release workflows
- Experience with Gradle, CocoaPods, Swift Package Manager, or similar tooling
Nice to have
- Experience with C++
- Experience building systems that run inside millions of devices and power security decisions behind the scenes
Benefits
- US‑level salaries globally
- Remote‑friendly in Europe
- Focus on outcomes rather than hours
Additional details
- Castle protects modern platforms from fraud and automated abuse
- Most people think of bot detection mostly as a web problem, but Castle protects both web applications and mobile apps
- For the web we ship a JavaScript agent
- For mobile, we ship SDKs for iOS and Android
- These SDKs run directly inside our customers’ applications and collect device signals, behavioral signals, sensor data, and other indicators to detect legitimate or automated (bot) users and abuse attempts such as fake account creation or automation
- Mobile SDKs operate in a more adversarial environment: attackers run emulators, patch apps, tamper with signals, and attempt to automate interactions
- Parts of the SDK also need to resist reverse engineering and manipulation
- The SDK runs inside other companies’ production apps, often used by millions of users; it must be fast, stable, and easy to integrate
- It cannot break builds or introduce noticeable performance overhead
- It must behave correctly across thousands of device models, OS versions, and application environments
- Building software under these constraints requires a different mindset than building a typical mobile application
- Castle is a small, profitable team building a real‑time trust layer for modern platforms
- Our mobile SDKs are a core part of that system, collecting signals used for device fingerprinting, behavioral analysis, and bot detection reliably at scale
- Originally posted on Himalayas