Mobile Engineer

Stack

Responsibilities

• ▹Design and improve the architecture of the 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
• ▹Ensure the SDK remains reliable as mobile platforms evolve

Requirements

• ▹Prior experience working on mobile SDKs or similar infrastructure that runs inside other applications
• ▹Strong experience with Kotlin and Swift, and ideally some C++
• ▹Understanding of mobile dependency management, build systems, and release workflows
• ▹Experience with Gradle, CocoaPods, Swift Package Manager, or similar tooling
• ▹Cares about performance, stability, and developer experience

Soft skills

About the company

Castle protects modern platforms from fraud and automated abuse, shipping a JavaScript agent for web and SDKs for iOS and Android that collect device and behavioral signals to detect bots and abuse. It is a small, profitable team building a real-time trust layer used inside apps with millions of users.