Mobile Architect - Outside IR35

Hydrogen UK Ltd; City Of London; Hybrid; GBP 70,000 - 110,000; Full time

Job summary

Hydrogen UK Ltd seeks an experienced mobile architect for an initial 8‑week piece of work with a strong chance of extension. The role is hybrid and outside IR35, focusing on reconstructing architecture of large systems from code and artefacts.

The candidate will drive platform decisions for iOS at depth while maintaining awareness of Android, supporting API/backend integration and governance across the mobile stack.

Qualifications

• Experience reconstructing architecture of large systems from code, interviews and artefacts.
• Fluency in structured modelling approaches (C4, arc42, UML, ADRs).

Responsibilities

• Define architecture characteristics and quality attributes and assess a system against them.
• Lead architectural reviews with CTO-level stakeholders.
• Ensure documentation-as-code and diagramming artifacts are kept up to date.

Skills

iOS depth

Android knowledge

Architecture patterns

Build & distribution

Documentation tooling

Executive stakeholder mgmt

Elicitation under resistance

Written clarity

English fluency

Cross‑platform stacks

Tools

Tuist

XcodeGen

XCFrameworks

SPM

Gradle

Job description

My client is looking for an experienced mobile architect to join their team on an initial 8 week piece of work with a good possibility to extend. This is a hybrid role and is outside of IR35.

Able to reconstruct architecture of large existing systems from code, interviews and incomplete artefacts - demonstrable, with examples; Fluency in structured modelling approach (C4, arc42, UML, ADRs). Documentation-as-code tooling, diagramming tools, Confluence/Miro.

Defining architecture characteristics and quality attributes, and assessing a system against them.

Platform bias: iOS depth expected. Must be conversant enough in Android to challenge and review docs and assessment findings.

iOS (primary depth)

• Swift, UIKit and SwiftUI in large production apps; understands the realities of a mixed UIKit/SwiftUI estate
• Modularisation at scale: SPM, Xcode workspaces, Tuist/XcodeGen, XCFrameworks, module boundary and dependency management
• Hands-on experience of architectural patterns in large production apps (MVVM, VIPER, TCA, Clean-style layering), and the ability to identify which one a codebase follows;
• Build, signing and distribution mechanics; profiling and performance analysis

Android (working knowledge)

• Kotlin, Jetpack Compose, Gradle multi-module builds: enough to read, question and validate, not necessarily to write

Backend, API and integration

• Mobile-to-backend integration patterns: BFF, API gateway, REST/GraphQL/gRPC, versioning and contract management
• Identity and authorisation: OAuth 2.0, OIDC, token lifecycle, session management, step-up authentication; FAPI and Open Banking awareness
• Understanding of how a bank's mobile app sits on top of core banking, payments and legacy estates, including mainframe-fronted services

Essential non-technical skills

• Executive stakeholder management: can hold a room with CTO-level stakeholders, present findings without softening them or turning them into an accusation
• Elicitation under resistance - gets useful answers from people who suspect they are being assessed
• Written clarity for mixed audiences
• Scope discipline: recognizes rabbit holes early and closes them protecting a fixed-price approach
• Independent judgement: willing to state a conclusion on partial evidence, and to label clearly where confidence is low
• Pace: comfortable producing a defensible first cut in week two for discussion and refining, rather than perfecting until week seven
• Fluent professional English, spoken and written

Nice to have

• Prior delivery inside a UK or EU retail bank, or comparably regulated environment
• Experience of a mobile platform modernisation or re-platforming programme, in either direction
• Cross-platform estates: Kotlin Multiplatform, React Native, hybrid/webview components
• Consultancy background; experience scoping and defending fixed-price work