Mobile Engineer

Hydrogen Group; City Of London; Hybrid; GBP 60,000 - 80,000; Full time

Job summary

Hydrogen Group is seeking an experienced Android Engineer for an initial 8-week contract, with potential extension. The role is hybrid and outside IR35, focusing on Kotlin, Jetpack Compose, and deep codebase analysis across Android, backend APIs, and security considerations.

The candidate will navigate large production codebases, dissect architectural patterns, and engage in rigorous analysis and collaboration with a client-facing team.

Qualifications

• Experience with Kotlin and modern Android in large production codebases.
• Experience with Jetpack Compose and legacy View-based UI.
• Ability to navigate large codebases and reconstruct runtime behavior.
• Experience with REST/GraphQL/gRPC APIs and OpenAPI.
• Familiarity with secure mobile practices including biometric auth and certificate pinning.
• Fluent professional English, spoken and written.

Responsibilities

• Read and map large, unfamiliar codebases quickly and systematically.
• Conduct code archaeology and analysis using static analysis and dependency graphs.
• Review CI/CD pipelines and instrument runtime behavior from logs and observability tools.
• Trace requests from UI through networking to backend services and back.

Skills

Kotlin

Jetpack Compose

MVVM

MVI

Clean architecture

Android debugging

Tools

Fastlane

Bitrise

GitHub Actions

Jenkins

Gradle

Xcode

Job description

My client has a need for an experienced Android Engineer to join their team for an initial 8 week piece of work with potential to extend. This is a hybrid role and is outside of IR35

Android (primary depth)

• Kotlin and modern Android in large production codebases; Jetpack Compose alongside legacy View-based UI
• Multi-module builds: reading, untangling and mapping them, including convention plugins and version catalogues
• DI frameworks and the ability to derive actual runtime structure from wiring
• Architectural patterns in practice (MVVM, MVI, Clean-style layering), and the ability to identify what a codebase genuinely does

Code archaeology and analysis

• Navigating an unfamiliar large codebase quickly and systematically
• Static analysis, dependency graph extraction, module dependency visualisation, code search at scale
• Reading CI/CD pipelines as a source of architectural truth: Fastlane, Bitrise, GitHub Actions, Jenkins, Gradle/Xcode build logic
• Reconstructing runtime behaviour from instrumentation, logging and observability tooling (Crashlytics, Sentry, Dynatrace, Firebase or similar)

Backend and API

• Tracing a request from UI through the mobile networking layer to the backend service and back
• REST/GraphQL/gRPC, OpenAPI and contract inspection, API gateway and BFF patterns
• OAuth 2.0 / OIDC token flows as implemented on device
• Third-party SDK inventory and assessment: analytics, payments, chat, fraud, marketing, feature flags

Banking-specific mobile concerns

• Secure storage, biometric authentication, device binding, certificate pinning as implemented in code
• Feature flags, remote config, phased/staged rollout, kill switches
• Offline behaviour, caching and state management, and what happens at the edges

Essential non-technical skills

• Structured interviewing - runs a technical interview that yields specifics rather than a tour of opinions, and captures it in a form the team can use
• Rigorous note-taking and traceability - findings can be traced back to a source; distinguishes what was observed in code from what someone said
• Collaborative, non-territorial - will be reviewing other engineers' work in front of them; needs to do it without triggering defensiveness
• Self-directed under time pressure - 8 weeks means little supervision and no ramp-up period
• Fluent professional English, spoken and written

Nice to have

• Financial services or other regulated-sector mobile delivery
• Kotlin Multiplatform, React Native, or hybrid/webview integration experience
• Diagramming from code: Structurizr, PlantUML, Mermaid, dependency-graph tooling
• Accessibility and performance profiling experience
• Consultancy or contracting background with multiple client environments
• iOS working knowledge (second depth) - Swift, SwiftUI/UIKit, SPM and Xcode project structure - sufficient to read the codebase and validate the Architect's iOS findings