FREELANCER PROFILE Senior Mobile Developer Native iOS (Swift) & Android (Kotlin) Kantar – Data Science Center (THX) — Groningen, Netherlands

About THX

THX is a division of Kantar and operates as a passive measurement platform across European and APAC markets. We combine ACR (audio content recognition), location tracking, and survey research to measure media exposure and advertising effectiveness for enterprise clients. Our consumer platform — THX. — recently launched in the APAC region (Japan) and we are actively expanding into additional markets beyond our current footprint in the Netherlands, Belgium, France, Germany, UK, Spain, and Italy.
Our Data Science Center in Groningen is a young, professional, and talented team of 15+ specialists who work fast and deliver on a global scale. We move quickly, we solve problems at their root, and we build technology that works across markets and cultures.

The Role

We are looking for a Senior Mobile Developer who is equally proficient in Kotlin (Android) and Swift (iOS). This is not a pure UI role. Our platform relies on deep native capabilities — audio content recognition running in the background, precise location tracking, power-efficient data collection, and tight integration with platform-specific APIs. We need someone who understands mobile infrastructure at a systems level.
The THX. platform performs passive measurement on users’ devices. This means our mobile applications need to handle background processing reliably, manage battery consumption carefully, operate within strict privacy regulations across different markets, and communicate efficiently with our backend services. You will be building and maintaining the native layer that makes all of this possible.

What We’re Looking For

Technical Expertise

• Production-level proficiency in both Swift (iOS) and Kotlin (Android), with a strong portfolio of shipped applications on both platforms
• Deep understanding of platform-specific lifecycle management, background execution models, permission handling, and the differences between iOS and Android in how they constrain long-running processes
• Experience with native audio processing, sensor APIs, or other hardware-level integrations is a strong advantage given our ACR and location tracking capabilities
• Strong command of RESTful API design and integration, including authentication flows (OAuth, JWT), efficient data serialization, request optimization, caching, and error recovery
• Proficiency in debugging and profiling native applications using Xcode Instruments, Android Studio Profiler, and platform-specific tools for memory, CPU, and network analysis
• Experience with CI/CD for mobile (Fastlane, GitHub Actions, Bitrise), automated testing strategies, and app store release management across both platforms

Infrastructure Understanding

• Working knowledge of cloud infrastructure (AWS preferred) and how mobile clients interact with backend services, CDNs, and data pipelines
• Understanding of push notification infrastructure (APNs, FCM), including silent pushes and their role in triggering background work
• Familiarity with privacy and data protection requirements across multiple jurisdictions (GDPR, APPI for Japan), and how these translate into technical implementation choices in the mobile layer
• Experience with crash reporting and observability tools (Firebase Crashlytics, Sentry) and how to use them to drive engineering decisions
• Understanding of data synchronization patterns, offline-first design, and conflict resolution between local and remote state

Mindset & Working Style

• Decisive: you assess situations quickly, form a clear opinion, and act on it — you don’t wait for someone to tell you what to do
• Consulting: you bring clarity to ambiguous situations, communicate trade-offs to both technical and non-technical stakeholders, and help the team make better decisions
• Solution engineer and fixer: when something is broken or underperforming, you diagnose it, fix it, and put guardrails in place to prevent recurrence
• Comfortable navigating the inherent complexity of maintaining two native platforms with different capabilities, constraints, and release cycles
• Autonomous but collaborative — you can own a workstream independently while staying aligned with the broader team direction

Practical Details

Engagement Freelance (via Octagon) Location Based in or around Groningen, Netherlands. Present in the Groningen office at least 3 days per week Duration Initial engagement 3–6 months, with extension based on roadmap needs and performance Availability Full-time preferred (32–40 hours/week) Start As soon as possible Rate Competitive, commensurate with experience — to be discussed  

Why This Engagement Is Interesting

This is not a standard app maintenance gig. You’ll be working on a platform that pushes the boundaries of what mobile devices can do passively — audio recognition, location intelligence, power-efficient background processing — across multiple countries with different regulatory environments. The technical challenges are real and the work has direct business impact for major clients.