Full Replatform of a Business App

Modernized with React Native.

Industry: HR Tech / SaaS
Duration: About 6 months (requirements through launch), plus ongoing operation
Team: 1 PM/engineer + 2 development engineers (Netsujo)
Scope: Requirements definition, architecture design, React Native implementation, release support, maintenance and operation
Technologies: React Native, TypeScript, iOS/Android cross-platform

Background

The client’s existing business app had accumulated features over many years, and the resulting codebase bloat had become a management issue: UX had degraded, and maintenance cost was climbing.

Separate native codebases for iOS and Android doubled the cost of every fix and led to inconsistent quality. Adding a new feature required investigating the impact on existing code, which had made release cycles longer and longer.

The challenges

Business: degraded UX and rising maintenance cost were slowing the business down — new features shipped late, widening the gap with competitors.
Technical: double maintenance from separate iOS/Android codebases, an undocumented legacy data structure, and an aging technology stack were compounding each other.
Organizational: whether to do a full replatform or an incremental rebuild, how to run the old app in parallel during migration, and how to hand off post-launch maintenance were all undecided — and the in-house engineering team had no spare capacity to drive a replatform.

Our approach

Separate iOS/Android development is a structural problem that doubles cost — incremental fixes cannot resolve it. We adopted React Native to build on a foundation that could also draw on web-development resources. Given how deep the existing technical debt was, we judged that a full replatform would have lower total cost than a staged migration.

During requirements definition, we inventoried every screen and feature in the current app and prioritized them on two axes — usage frequency and business impact — narrowing the replatform scope by clearly identifying features that were no longer used.

Requirements definition: identifying issues in the current system, user interviews, and prioritization
Architecture design: cross-platform design using React Native
Implementation: a full replatform on a single iOS/Android codebase
Data migration: reverse-engineering the old schema and building migration scripts
Release support: app-store submission and post-launch stabilization
Maintenance and operation: ongoing feature additions on the unified codebase

Results

Key takeaways

Completed the move to a modern technology stack (React Native)
Consolidated maintenance into a single codebase, eliminating duplicate fixes
Improved UX through a UI refresh, well received by on-site staff
Shortened release cycles, speeding up new-feature delivery
Continued as an ongoing partner through the maintenance and operation phase

Before / after

Before: Separate iOS/Android codebases doubled fix costs; legacy UX and lengthening release cycles were slowing the business down.
After: Consolidated onto a single React Native codebase, cutting maintenance effort while refreshing the UI, with Netsujo continuing to support the project after launch.

Who this fits

Technical debt in an existing app is holding back business speed
iOS and Android are maintained as separate codebases, doubling cost
Considering a replatform but not yet able to get into requirements
Want a partner who works alongside you with a PM mindset, not one that simply takes an outsourced brief
Want the design to consider post-launch maintenance from the start

To talk through a similar replatform or app-modernization project.