Interview Format Overview
This one-hour initial call will focus on understanding your background and experience in depth. The interviewers will have read your CV, so this is an opportunity to elaborate on your contributions. They’re interested in recent projects, implementation details, trade-offs made, and reflections. The interview will be conversational rather than scripted, covering technical challenges, customer-facing app development, and cross-functional team experience.
Experience 1: Frontend Migration from Vue.js to React
Overview: At Pfida, you transformed a problematic finance application by implementing a microfrontends approach to migrate from Vue.js to React while maintaining compliance with financial regulations.
STARR Answer:
Situation: At Pfida, I inherited a finance application built with Vue.js that was causing significant issues. The application was critical for financial operations but had accumulated technical debt, was difficult to maintain, and was generating numerous data-related support tickets.
Task: I needed to transform this application to a more maintainable technology stack (React) without disrupting ongoing operations or compromising financial regulatory compliance. The challenge was to perform this migration without a complete rewrite, which would have been too risky and time-consuming.
Action: I designed and implemented a microfrontends architecture that allowed for gradual, component-by-component migration. This approach involved:
- Creating a wrapper application that could host both Vue.js and React components simultaneously
- Establishing clear boundaries between different functional areas
- Implementing a shared state management solution that worked across both frameworks
- Prioritizing the migration of the most problematic areas first
- Setting up comprehensive testing to ensure functional equivalence before and after migration
- Documenting the migration process and best practices for the team
Result: This strategic approach achieved full compliance with financial regulations while decreasing data-related support tickets by 78%. More importantly, it expanded our development capacity by enabling React-proficient backend developers to contribute to the frontend. This not only accelerated the migration but also broadened our hiring prospects for new team members.
Reflection: In hindsight, this project taught me the value of incremental transformation over high-risk rewrites. I learned that technical migrations must be driven by business metrics (like support ticket reduction) rather than just technical preferences. If I were to approach a similar challenge again, I would establish even more granular metrics to track progress and potentially introduce more automated testing earlier in the process.
Talking Points:
- The technical decision-making process that led to choosing microfrontends for the migration strategy
- How I managed the knowledge transfer between team members with different framework expertise
- Specific React patterns I implemented to improve maintainability compared to the previous architecture
- How I balanced immediate business needs with long-term technical health
- The documentation approach that enabled successful knowledge sharing across the team
Experience 2: Multi-tenancy Solution for White-labeling
Overview: You engineered a frontend multi-tenancy solution at Pfida that enabled white-labeling, feature configuration, and dynamic theming, opening new revenue streams through partner banks.
STARR Answer:
Situation: Pfida had identified a significant business opportunity to offer its financial services platform to partner banks, but our single-tenant architecture couldn’t support different branding, feature sets, or user experiences required by different partners.
Task: I was tasked with developing a multi-tenancy solution that would allow the platform to be white-labeled for different financial institutions while maintaining a single codebase, enabling partner-specific configurations, and supporting dynamic theming.
Action: I:
- Designed a configuration-driven architecture that determined feature availability, branding, and UI elements based on tenant identity
- Implemented a theming system using CSS variables and dynamic style loading to support partner branding
- Built a feature flagging system that allowed granular control over which capabilities were available to each tenant
- Developed an asset management approach for handling tenant-specific images, icons, and other media. Essentially, they were stored in S3 bucket and we just uploaded them there. We then were able to grab them dynamically using tenantid to access correct bucket.
Result: This solution allowed the business to offer its services to partner banks, unlocking a significant new revenue stream. Within a short period of time, we successfully onboarded a big partner bank with their distinct branding and feature sets. The architecture proved scalable and required minimal maintenance overhead as new partners were added.
Reflection: This project reinforced the importance of designing for extensibility from the start. While the initial implementation took longer than a simpler approach might have, the long-term business value far exceeded the investment. If I were to do it again, I would build even more robust tooling around tenant configuration management to reduce the operational complexity of onboarding new partners.
Talking Points:
- The technical architecture that enabled efficient multi-tenancy without code duplication
- How I approached the theming system to balance flexibility with performance
- The process for testing across multiple tenant configurations to ensure reliability
- Considerations for data isolation and security in a multi-tenant environment
- How the technical implementation aligned with business development and onboarding processes
Experience 3: Design System Implementation
Overview: You implemented a company-wide design system using TailwindCSS, Radix UI, Storybook, and Chromatic, improving delivery speed and brand consistency.
STARR Answer:
Situation: At Pfida, our UI development was inconsistent across products, leading to brand inconsistency, duplicated effort, and longer development cycles. Each team was implementing similar components differently, which created a fragmented user experience and made maintenance challenging.
Task: I needed to create a unified design system that would standardize component development, improve visual consistency, reduce development time, and ensure accessibility across our applications.
Action: I:
- Collaborated with designers to audit existing UI patterns and establish a component inventory
- Selected TailwindCSS for styling to provide consistency with flexibility
- Integrated Radix UI primitives to ensure accessible, behavior-consistent components
- Set up Storybook as a development environment and documentation tool
- Implemented Chromatic for visual regression testing and review workflows
- Created a component development process that included design reviews, accessibility checks
- Organized components into logical categories with clear usage guidelines
- Established a versioning strategy to manage changes without breaking existing implementations
Result: The implementation resulted in faster feature delivery (30% reduction in UI development time), enhanced brand consistency across products, and significantly reduced regression issues. The design system became a central resource for both designers and developers, improving collaboration and communication. Additionally, our accessibility compliance improved dramatically as all new components adhered to WCAG standards.
Reflection: The design system project taught me that technical solutions alone aren’t enough—adoption requires excellent documentation, advocacy, and demonstrable benefits to teams. In future implementations, I would involve more diverse stakeholders earlier in the process and create more comprehensive onboarding materials to accelerate adoption.
Talking Points:
- The process of balancing design flexibility with standardization
- How I approached component API design to maximize reusability
- The governance model established to maintain and evolve the design system
- Performance considerations and optimizations in the component library
- How the design system facilitated better designer-developer collaboration
Experience 4: Backend-for-Frontend Pattern with AWS Lambdas
Overview: You implemented a backend-for-frontend pattern using AWS Lambdas to streamline development and shift business logic, improving feature delivery speed.
STARR Answer:
Situation: At Pfida, our frontend applications were directly consuming multiple microservices APIs, which created tight coupling, led to over-fetching of data, and pushed business logic into the frontend. This made feature development slower and more error-prone, especially as our microservice architecture expanded.
Task: I needed to design and implement an architecture that would decouple our frontend applications from the underlying microservices, reduce network overhead, simplify frontend logic, and accelerate feature development.
Action: I:
- Designed a Backend-for-Frontend (BFF) pattern using AWS Lambda functions dedicated to specific frontend needs
- Created API endpoints that aggregated data from multiple microservices in single requests
- Implemented caching strategies appropriate for different data types to improve performance
- Moved business logic from frontend applications to the BFF layer
- Set up comprehensive monitoring and logging for the new API layer
- Created documentation and examples to help other developers adopt the pattern
Result: This architectural change reduced over-fetching of data, accelerated feature delivery by approximately 40%, and standardized API consumption patterns company-wide. Frontend code became simpler and more focused on presentation concerns, while business logic was properly encapsulated in the backend. The architecture also provided a clear separation of concerns that made it easier to modify individual services without impacting the frontend.
Reflection: This project highlighted the importance of thoughtful API design and the value of intermediate layers in a distributed architecture. If implementing again, I would establish more formal API contracts from the beginning and invest more in automated testing tools specific to this pattern.
Talking Points:
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The decision-making process that led to choosing AWS Lambdas for this implementation
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How I approached API design to best serve frontend needs
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Performance optimizations implemented in the BFF layer
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Security considerations when implementing this pattern
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How this pattern facilitated better separation of concerns across the stack
Experience 5: Ephemeral Environments Implementation
Overview
Implementation of ephemeral environments using AWS, Terraform and GitHub Actions at Pfida, providing non-technical stakeholders with visual previews of changes for easier feedback and improving review efficiency by 25%.
STARR Method Answer
Situation
At Pfida, we were experiencing friction in our development workflow. Non-technical stakeholders (product managers, designers, and business leadership) had difficulty understanding proposed changes from looking at pull requests. They needed to wait until features were deployed to staging environments to provide feedback, which often led to late-stage change requests and delayed releases.
Task
I was tasked with finding a solution that would allow stakeholders to preview changes earlier in the development process without requiring technical knowledge or local environment setup. The goal was to streamline our feedback cycle and reduce the overall time from development to approval.
Action
I designed and implemented an ephemeral environment system with the following components:
- Created a Terraform configuration to provision isolated AWS resources (including S3 buckets, CloudFront distributions, and Route53 DNS entries) for each pull request
- Developed GitHub Actions workflows that would:
- Detect when a pull request was opened or updated
- Build the application with the changes
- Deploy to the provisioned infrastructure
- Generate a unique URL for stakeholders to access
- Post the URL as a comment on the pull request
- Implemented automatic cleanup processes to destroy environments when pull requests were closed or merged
- Created documentation explaining how to use the system and integrated it into our onboarding materials
Result
The implementation delivered significant benefits:
- Reduced feedback cycle time by 25% as measured by time from pull request creation to approval
- Improved cross-functional collaboration
- Decreased late-stage change requests by approximately 40%
- Saved developer time previously spent manually showing changes to stakeholders
- Reduced infrastructure costs compared to maintaining permanent staging environments for each feature
- Improved the quality of feedback as stakeholders could interact with actual working features
Reflection
This project taught me the importance of removing technical barriers for non-technical team members. For future implementations, maybe instead of building it by myself, I would leverage platforms that already provide with such functionality like Cloudflare, so we don’t have to worry about building this infrastructure by yourselves, and probably has more functionality, where you can roll things back etc. This experience reinforced my belief that investing in developer experience and cross-team collaboration tools pays dividends in product quality and team efficiency.
Talking Points
- The technical architecture decisions between different AWS services and why certain choices were made
- How we managed security concerns with ephemeral environments and sensitive data
- Cost optimization strategies when dynamically creating cloud resources
- How the ephemeral environments integrated with our CI/CD pipeline and testing strategy
- Specific metrics we used to measure the 25% improvement in review efficiency
Experience 6: Contract-Driven Development Implementation
Overview
Implementation of contract-driven development at Pfida with auto-generating MSW mock APIs, TanStack Query hooks, and Zod schemas to streamline parallel development and promote isolated testing with Chromatic (Playwright) and React Testing Library.
STARR Method Answer
Situation
Our engineering team at Pfida was facing challenges with frontend-backend integration. The frontend and backend teams were working in parallel, but frequent API changes were causing integration issues, blocking frontend development, and requiring significant rework. Testing was inconsistent, with mock data varying between developers and test environments.
Task
I was challenged to improve our development workflow to allow frontend and backend teams to work more independently while ensuring compatibility when integrating. Additionally, we needed to enhance our testing approach to catch integration issues earlier in the development cycle.
Action
I led the implementation of a contract-driven development approach:
- Designed and implemented a schema-first API development process using Zod for runtime type validation
- Created a code generation pipeline that:
- Generated TypeScript types from OpenAPI schemas schemas that we did write in the backend first with Zod and OpenAPI plugin
- Auto-generated TanStack Query hooks for the frontend based on API contracts
- Created MSW (Mock Service Worker) handlers automatically from the same contracts
- Built a central repository of contracts that served as the single source of truth for API interfaces and documentation
- Implemented integration testing using the generated mocks with Chromatic for visual regression testing and Playwright for end-to-end testing for critical paths
Result
The implementation delivered substantial improvements:
- Reduced integration issues by approximately 65% as measured by related bug tickets
- Enabled true parallel development, with frontend and backend teams able to work independently
- Improved test coverage and reliability with consistent mock data
- Accelerated feature delivery timeframes by eliminating waiting periods between frontend and backend work
- Enhanced developer experience with type safety and auto-generated API clients
Reflection
This project reinforced the value of investing in developer tooling and establishing clear contracts between systems. If I were to approach this again, I would have started with a smaller scope to demonstrate value before rolling out to the entire codebase. I would also have included more comprehensive documentation and examples from the beginning. For future implementations, I would explore adding automatic API versioning and more sophisticated contract first approach with Pact testing, but I think this was not really needed for our size of the team. This taught me that you can pick and choose from methodologies, and you don’t have to roll out the whole thing just like the book says. Code quality is important, but it should not sacrifice velocity and Devex.
Talking Points
- The decision-making process behind choosing Zod over alternatives like JSON Schema or OpenAPI
- How we handled contract versioning and backward compatibility
- Integration of the contract system with our CI/CD pipeline
- Specific examples of how this approach caught integration issues before they reached production
- How we measured the success of the implementation with metrics
- Managing the learning curve and adoption across teams
Experience 7: React Admin Platform Development
Overview
Development of a React-based admin platform with a microservices backend (AWS Lambdas and PostgreSQL) at Pfida, freeing the CTO from manual Python scripts and enabling non-technical stakeholders to update data independently.
STARR Method Answer
Situation
At Pfida, our CTO was spending significant time running manual Python scripts to update data in the application. This created a bottleneck as other stakeholders needed to request changes through the CTO, leading to delays and increased workload on the technical leadership. Additionally, there was no audit trail of changes, creating potential compliance issues.
Task
I was assigned to create a self-service admin platform that would allow non-technical stakeholders to manage their own data and configurations without requiring technical expertise or access to production systems. The solution needed to be secure, auditable, and user-friendly while reducing the operational burden on the CTO.
Action
I led the development of a comprehensive admin platform:
- Designed a React frontend with an intuitive interface focused on usability for non-technical users
- Implemented a microservices backend architecture using AWS Lambda functions to handle tasks
- Created a PostgreSQL database schema with audit logging for all changes with pgaudit
- Built a role-based access control system to ensure users could only access appropriate sections
- Developed a workflow system for changes requiring approval
- Implemented comprehensive validation to prevent data integrity issues
- Created automated testing for both frontend and backend components (more like behavioural test that reflexted the business logic rather than how it should be working from a technical point of view)
- Implemented ssentry and distributed tracing for catching errors
- Conducted sessions with stakeholders to refine the interface
- Created documentation so that internal stakeholders could reference when using the app
Result
The admin platform delivered significant improvements:
- Reduced the CTO’s time spent on administrative tasks
- Enabled non-technical stakeholders to make changes independently, increasing their autonomy
- Improved change implementation time from days to minutes for most common operations
- Created a comprehensive audit trail for compliance purposes
- Reduced errors in configuration changes due to built-in validation
- Improved security by eliminating the need for direct database access to make changes
- Received positive feedback from stakeholders about ease of use
Reflection
This project highlighted the importance of empowering users with self-service tools while maintaining appropriate guardrails. In retrospect, I would have involved end-users earlier in the design process to better understand their mental models. At the beginning, we implemented some features that were not really reflecting how they work so we had to change them. We learned from that and changed it. The experience taught me that technical solutions that remove bottlenecks and empower non-technical users can have outsized business impact beyond the immediate technical improvements.
Talking Points
- The technical architecture decisions between a monolithic vs. microservices approach
- UI/UX considerations for creating interfaces for non-technical users
- Security measures implemented to protect sensitive operations
- How we approached testing for both the React frontend and AWS Lambda functions
- Performance optimizations for the admin interface
- How we managed feature prioritization based on stakeholder needs
Interview Tips
- Prepare specific technical details: Monzo interviewers specifically mention they want to hear about technical details such as data structures, language choices, and performance/reliability trade-offs. For each example you discuss, have ready explanations about specific technical decisions you made and why.
- Focus on cross-functional collaboration: The job description emphasizes working in squads alongside product managers, designers, and other roles. Highlight examples of effective cross-disciplinary collaboration in your projects.
- Emphasize user experience focus: Monzo values providing great user experiences. When discussing your projects, emphasize how your technical decisions improved user experience, not just code quality.
- Be ready to discuss trade-offs: The interview process specifically mentions discussing what trade-offs were made and what you’d do differently in hindsight. For each project, prepare thoughts on alternative approaches you considered and why you made specific choices.
- Connect your experience to Monzo’s tech stack: While not explicitly required to know their stack, demonstrating how your experience with React, TypeScript and modern JS frameworks relates to their needs would be valuable. The job description mentions they use React, so emphasize your React experience.
Why do you want to work with us
- Values align very well. I care about the customers/users and this is what you care about too.
- I also have a feeling that I might have the same mindset as others at Monzo, which is focusing on the things that have the biggest impact for customers, team and the business overall.
- I spent some time going through your blog, and I got the feeling that there’s a great engineering culture, good processes in place, colaborative and people try to help each other
Can you share an example of when you collaborated with cross-functional teams (e.g., designers, backend engineers, product managers) to deliver a project? What challenges did you face and how did you overcome them?
- Refer to the Admin Panel
- Talk about creating simple jira board so that everyone was able to see what is the status of the project and be able to contribute to it as well, and document what we discuss
- Every person had different perception/mental model of how things are working
Tell us about a time when you worked closely with backend engineers to design or integrate an API for a new feature. What were some of the trade-offs you had to consider?
- Spreadsheet upload
- Refer to contract first approach
Describe a scenario where you had to balance fast development speed with maintaining high code quality. How did you approach this trade-off?
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refer to multi tenanting
Can you discuss your experience with modern JavaScript frameworks (like React, Vue, or Angular) and how you decide which tool is best suited for a project?
I have extensive experience with React, a bit with Vue and none with others.
I prefer React for most applications due to its extensive tooling and community support. It scales well when building SPAs or websites where quite a lot changes. React is not a perfect solution for everything, and for more static app, I would probaby use Astro or something similar.
Decision Criteria:
- Project Size: React for large, complex apps; Vue for smaller, faster-to-market solutions.
- Team Familiarity: Align with team expertise to minimise ramp-up time.
- Performance Needs: Consider SSR (Next.js for React) or SPA where appropriate.
Share an example of how you ensured performance, accessibility, and security in a web application you built.
- Refer to the WWebapp revamp
- Accessibility
- Use Storybook for testing accessibility
- Ensure that font size and contrast are correct
- Security
- Endpoint behind auth, rate limiting
- Rotation of passwords to a db
- Performance
- index DB at ANS
- React Native App, Ans, Animations, memoisation of state
Tell us about a time when you iterated on a feature based on user feedback and data insights. How did you incorporate these insights into your development process?
A internal app had a feature where you can upload spreadsheets with financial data. It was a bit problematic, because mutation of data uploaded
What is your working style?
- I value open communication with cross-functional teams, ensuring alignment between product, design, and engineering.
- I thrive in agile environments, iterating based on feedback and adapting to evolving requirements.
- I balance autonomy and collaboration, proactively driving tasks while seeking input where it adds value.
- I enjoy working with data-driven insights to guide decisions and iterate towards improving user experience.
- parmatic decision making
Question: What considerations do you have for web accessibility in your projects?
- Semantic HTML: Ensuring correct use of HTML tags to provide meaning to assistive technologies.
- Keyboard Navigation: Guaranteeing full keyboard operability and focus management.
- ARIA Attributes: Using ARIA only where native HTML doesn’t provide the required functionality.
- Colour Contrast & Text Scaling: Meeting contrast ratios and supporting text resizing without breaking layouts.
- Continuous Testing: I use Axe and Lighthouse to catch accessibility regressions.
Question: How do you approach testing in your frontend applications?
- Unit testing: pure fnctions and not 100% coverage. 90% is fine
- Integration tests: Integration with backend APIs with MSW mocks
- E2E testS: Using plightwirght to simulate user behaviour for critical parts of the apps
- Visual Tests: For UI components that are reusable
Question: What’s your experience with performance optimization for web applications?
- Critical Rendering Path Optimisation: Reducing First Contentful Paint (FCP) by optimising CSS, JS, and images.
- Code Splitting & Lazy Loading: Using dynamic imports to reduce initial page load.
- Caching Strategies: Implementing HTTP caching, service workers, and CDN usage. n
- Reducing JavaScript Payload: Analysing and eliminating unnecessary packages using Bundle Analyzer.
- Runtime Performance: Profiling and fixing long tasks to improve responsiveness.
Question: How do you stay updated with the latest frontend technologies and best practices?
- Newsletter
- Youtube
- Blogs
- Conferences
- Meetups
- Reading Official Documentation: Following release notes for React, Next.js, and relevant libraries.
- Community Engagement: Participating in GitHub discussions, forums, and tech communities.
- Following Thought Leaders: Keeping up with frontend thought leaders and blogs like CSS Tricks, Smashing Magazine, and JavaScript Weekly.
- Hands-on Learning: Building proof-of-concept projects to experiment with new technologies.
Questions for You to Ask Them
- “How is the engineering team structured at Monzo, particularly in the web development area?”
- “What are the biggest technical challenges your team is currently facing?”
- “Can you tell me more about how engineers collaborate with designers and product managers at Monzo?”
- “How do you approach technical decision-making at Monzo? Who’s involved and what’s the process like?”
- “What does the career progression path look like for engineers at Monzo?”
- “How do you balance feature development with technical debt and infrastructure improvements?”
- “What technologies in your stack are you most excited about or planning to adopt in the near future?”
- “How do you approach monitoring and observability for applications?”