What is a Mobile Engineer?

A Mobile Engineer at Poshmark owns the end-to-end experience of our iOS and Android apps that millions of community members use to browse, buy, and sell every day. You translate product strategy into performant, reliable, and beautiful mobile experiences, balancing feature velocity, quality, and scalability. Your code directly shapes core surfaces like the home feed, search & discovery, listing flow, checkout, notifications, and social features (e.g., follows, shares, comments).

This role is critical because the mobile app is Poshmark’s primary customer touchpoint and revenue driver. You will work closely with Product, Design, Data, and Backend teams to deliver features, optimize conversion funnels, and maintain a seamless, social commerce experience. Expect to contribute to clean architecture, offline readiness, robust analytics, and release health—areas where excellence translates into measurable business impact.

You’ll find this role compelling if you enjoy turning ambiguous customer needs into pragmatic technical solutions, collaborating across disciplines, and operating with ownership. It’s hands-on, high-visibility work: shipping well-architected Kotlin/Swift code, improving performance, and raising the bar for our app quality and team practices.

Getting Ready for Your Interviews

Your preparation should focus on three pillars: coding fluency in the platform language, mobile-specific system design, and practical product thinking. You will face a mix of LeetCode-style problems (often easy-to-medium), architecture discussions (Clean Architecture, SOLID, MVVM/MVI), and behavioral signals around collaboration and ownership. Prepare to explain trade-offs, show pragmatic judgment, and communicate clearly under time constraints.

• Role-related Knowledge (Technical/Domain Skills) – Interviewers assess your command of the mobile stack (Android/iOS), including language fluency (Kotlin/Swift, occasionally Objective‑C), lifecycle mastery, networking, persistence, and concurrency. Demonstrate understanding through code, concrete examples from shipped features, and clear articulation of architecture choices and best practices.

• Problem-Solving Ability (How you approach challenges) – Expect straightforward algorithmic prompts (strings, arrays, parsing) and debugging scenarios tied to mobile behaviors (lifecycle, threading, memory). Show your process: ask clarifying questions, state assumptions, outline trade-offs, implement cleanly, and validate with tests and edge cases.

• Leadership (Influence without authority) – Even as an IC, you will influence design decisions, mentor peers, and improve team practices (code reviews, CI/CD, testing). Interviewers look for calm prioritization, data-driven decision-making, and a bias for action when requirements are ambiguous or evolving.

• Culture Fit (Collaboration, communication, ambiguity) – Poshmark values a community-first mindset and ownership. Show empathy for users, align with product goals, and demonstrate how you adapt, communicate proactively, and handle feedback—even when opinions differ.

Interview Process Overview

You can expect a focused, fast-moving process that emphasizes practical skills over trick questions. The cadence typically starts with a recruiter conversation, followed by a hands-on technical screen, and culminates in a collaborative onsite (virtual or in-person). The tone is professional and pragmatic: interviewers aim to simulate how you would work day-to-day on our codebase and with our teams.

Rigor is calibrated to the role level. Coding assessments skew towards clear, correct solutions in the platform language with strong communication. Architecture conversations prioritize clean boundaries, testability, and maintainability, while behavioral interviews probe for ownership, collaboration, and resilience. Expect a respectful pace, but be ready to drive clarity and confirm expectations—doing so signals seniority.

This timeline illustrates the typical flow from recruiter screen to technical assessment and a consolidated onsite loop. Use it to plan your prep energy: practice language-specific coding ahead of the screen, then allocate time for architecture and behavioral depth before the onsite. Between stages, confirm logistics, language expectations, and any pre-work to avoid surprises.

Deep Dive into Evaluation Areas

Coding Fluency in Platform Language

This is foundational. You will implement solutions in Kotlin (Android) or Swift/Objective‑C (iOS) in a shared editor (e.g., CoderPad). Problems are typically easy-to-medium and often string/array manipulation, but interviewers evaluate more than correctness: readability, idiomatic usage, and deliberate testing matter.

• Be ready to go over:

  • Core language constructs: collections, optionals/nullability, extension functions, data classes/structs, generics
  • Algorithmic basics: string parsing, hash maps/sets, two-pointers, stacks/queues
  • Complexity & testing: time/space trade-offs, edge cases, unit-test-like validation
  • Advanced concepts (less common): Swift async/await, Kotlin coroutines/Flow, functional patterns, immutability

• Example questions or scenarios:

  • "Given a string, compress consecutive characters (case-sensitive) and return the shorter of original vs. compressed."
  • "Implement a function to check if two strings are isomorphic."
  • "Refactor an imperative loop into idiomatic Kotlin/Swift using standard library functions."
  • "Write-and-talk: explain your choice of data structures and test edge cases (empty input, Unicode, large input)."

Mobile Architecture & System Design

Here, interviewers look for well-structured, testable architectures that scale with product complexity. Expect to discuss Clean Architecture, SOLID, and patterns like MVVM/MVI (Android) or MVVM with Combine/async‑await (iOS). You should frame data flow clearly, isolate side effects, and design for feature modularity.

• Be ready to go over:

  • Layering & boundaries: presentation/domain/data separation, dependency inversion, DI frameworks
  • State management: flows/LiveData/StateFlow, reducers, unidirectional data flow
  • Offline readiness: caching, synchronization, conflict resolution, retry strategies
  • Advanced concepts (less common): feature modules, dynamic delivery, GraphQL clients, schema evolution, plugin-driven architectures

• Example questions or scenarios:

  • "Design the Poshmark home feed with offline support, pagination, and error recovery."
  • "How would you apply SOLID to the listing creation flow to improve testability?"
  • "Compare MVVM vs. MVI for a chat/notifications screen; when would you choose each?"

Performance, Reliability, and the Mobile Runtime

Interviews may probe your ability to profile, diagnose, and optimize app performance. You must recognize lifecycle pitfalls, memory leaks, and concurrency hazards, and you should be comfortable with platform tools.

• Be ready to go over:

  • Performance fundamentals: layout/rendering cost, overdraw, diffing lists, image loading
  • Memory & threading: ARC and retain cycles (iOS), leaks and coroutines scopes (Android), ANR/hangs prevention
  • Startup & stability: cold/warm start strategies, crash triage, background work constraints
  • Advanced concepts (less common): Instruments, Systrace, ANR reports, symbolication, structured concurrency patterns

• Example questions or scenarios:

  • "You notice jank while scrolling the feed—how do you diagnose and fix it?"
  • "Explain a real incident you resolved that involved lifecycle misuse and a memory leak."
  • "Walk through reducing cold-start time by 20%."

Networking, Data, and Observability

You will be evaluated on how you design resilient data flows with REST/GraphQL, persistence, and analytics. Expect to justify serialization choices, caching policies, and error handling strategies that protect the user experience.

• Be ready to go over:

  • Networking: request modeling, pagination, retries/backoff, auth/refresh tokens
  • Persistence: Room/SQLDelight (Android), Core Data/Realm (iOS), schema migrations
  • Observability: analytics events, funnel instrumentation, logging, feature flags, A/B tests
  • Advanced concepts (less common): background sync constraints, conflict resolution, end-to-end idempotency

• Example questions or scenarios:

  • "Design an offline-first listing flow with draft autosave and conflict resolution on publish."
  • "How would you instrument analytics for the checkout funnel to detect drop-offs?"
  • "Discuss pros/cons of JSON vs. Protobuf for mobile payloads at Poshmark scale."

Collaboration, Product Sense, and Delivery

This area validates how you work with PM/Design/Backend to ship value predictably. You’ll discuss scoping, negotiating trade-offs, and ensuring quality through reviews, testing, and CI/CD. Bring concrete examples demonstrating ownership from ideation to release and iteration.

• Be ready to go over:

  • Discovery to delivery: slicing features, phasing risky work, design handoffs
  • Quality gates: code review standards, unit/UI tests, feature toggles, rollout strategies
  • Conflict & feedback: aligning when opinions differ, making decisions transparent
  • Advanced concepts (less common): incident response, release automation, canary rollouts

• Example questions or scenarios:

  • "Tell me about a time you disagreed with a reviewer’s approach—what did you do?"
  • "How would you phase an experimental social feature to derisk engagement impact?"
  • "Walk through your CI/CD setup and how you keep build health green."

This visualization highlights the most frequent focus areas in recent interviews: platform languages (Kotlin/Swift/Objective‑C), string/array coding, Clean Architecture and SOLID, MVVM, networking/persistence, and lifecycle/performance. Use it to prioritize your prep: practice platform-language coding first, then deepen architecture and runtime expertise.

Key Responsibilities

You will own features from design to release in our mobile apps, ensuring high-quality, maintainable code and a smooth user experience. Day to day, you will collaborate with Product on scope, Design on UX, and Backend on API contracts, while maintaining a healthy codebase and reliable releases.

• Build, test, and ship features across discovery, listing, checkout, social interactions, and notifications.
• Apply Clean Architecture, SOLID, and MVVM/MVI to keep code modular, testable, and scalable.
• Ensure app performance, stability, and accessibility; proactively address regressions and tech debt.
• Partner on API design, analytics instrumentation, and observability for data-driven iteration.
• Contribute to code reviews, testing strategy, CI/CD, and release management.

Your work will include operational excellence (alerting, crash triage), product iteration (A/B tests, feature flags), and architectural improvements (modularization, offline strategies) that keep the app fast and reliable at scale.

Role Requirements & Qualifications

We look for engineers who combine strong platform skills with pragmatic product thinking. You should demonstrate fluency in the native language, a solid grasp of mobile architecture, and the ability to deliver high-quality features in a collaborative environment.

• Must-have technical skills

  • Android: Kotlin, coroutines/Flow, AndroidX, Jetpack (ViewModel, Navigation, Room), Retrofit/OkHttp, DI (Hilt/Dagger)
  • iOS: Swift, Swift Concurrency (async/await), Combine (or equivalent), UIKit/SwiftUI, URLSession, persistence (Core Data/Realm), DI patterns
  • Testing (unit/UI), CI/CD, analytics, feature flags, crash reporting; strong Git practices

• Experience

  • Track record of shipping production mobile apps or major features at scale
  • Demonstrated use of Clean Architecture, SOLID, and MVVM/MVI with clear layering
  • Performance tuning, debugging, and lifecycle expertise

• Soft skills

  • Clear communication, collaborative problem-solving, and user empathy
  • Ownership mindset: proactive risk management, data-driven decisions, crisp trade-off discussions

• Nice-to-haves

  • Objective‑C or Java interoperability, GraphQL clients, offline-first architectures
  • Modularization/Dynamic Feature Delivery, build performance tuning, release automation

This snapshot provides current compensation ranges for Mobile Engineers by level and location where available. Use it to calibrate expectations and prepare data-driven compensation questions for your recruiter; ranges vary by market, experience, and interview performance.

Common Interview Questions

Expect a blend of coding, architecture, and behavioral questions aligned to our app’s core surfaces and engineering practices.

Coding and Language Fluency

Short, focused problems where correctness, clarity, and idiomatic language use matter.

• Implement a function to compress strings with counts (e.g., "aaabb" -> "a3b2") and return the shorter of the two.
• Determine if a string has all unique characters without extra space.
• Reverse words in a sentence while preserving whitespace.
• Merge two sorted arrays and analyze time/space complexity.
• Refactor a nested-loop solution into O(n) using a hash map; explain trade-offs.

Mobile Architecture and Design

Probe your ability to structure apps for scale and testability.

• Walk me through applying SOLID principles to the listing creation flow.
• Compare MVVM vs. MVI for a notifications screen; what trade-offs do you see?
• Design an offline-first feed with pagination, retries, and conflict resolution.
• How would you organize modules to enable faster builds and independent feature ownership?
• Describe how you’d evolve an API contract for a new filter without breaking older clients.

Performance and Lifecycle

Assess runtime understanding, debugging, and optimization.

• How do you diagnose and fix jank in a complex RecyclerView/List?
• Explain a memory leak you found and how you prevented it (retain cycles, lifecycle scope).
• Strategies to reduce cold-start time by 20% without major refactors?
• How do you prevent ANRs/hangs during heavy I/O?
• What metrics and alerts would you put in place to monitor release health?

Networking, Data, and Observability

Focus on resilient data flows and product measurement.

• Design a robust retry/backoff mechanism with exponential delay and jitter.
• Core Data vs. Realm (or Room vs. SQLDelight): when and why?
• How do you structure analytics for checkout to detect drop-offs by step?
• What is your approach to versioned migrations and backward compatibility?
• How do you secure tokens and handle refresh flows gracefully?

Behavioral and Collaboration

Understand how you navigate ambiguity and influence outcomes.

• Tell me about a time an interviewer/reviewer wanted a different approach—how did you handle it?
• Describe a project where you balanced shipping speed with architectural quality.
• How do you mentor teammates on code quality and testing?
• Share a situation where requirements changed late—what did you do?
• How do you give and receive tough feedback effectively?

These questions are based on real interview experiences from candidates who interviewed at this company. You can practice answering them interactively on Dataford to better prepare for your interview.

Frequently Asked Questions

Q: How difficult are the coding rounds?
Most candidates report easy-to-medium difficulty, often focused on strings/arrays. Don’t underestimate them—interviewers expect clean, idiomatic solutions in Kotlin/Swift and thoughtful edge-case handling.

Q: Do I need to code in Kotlin/Swift, or can I use Python/Java?
Plan to use the platform language. Several candidates were penalized for using non-native languages even after solving correctly. Confirm language expectations at the start and default to Kotlin/Swift.

Q: How should I prepare for architecture conversations?
Review Clean Architecture, SOLID, and MVVM/MVI. Prepare a recent feature you built, diagram the layers, explain dependencies and data flow, and discuss trade-offs you made for testability and delivery speed.

Q: What’s the typical timeline?
Processes often complete within 2–3 weeks, depending on scheduling. Keep momentum by being responsive, confirming next steps after each round, and clarifying any pre-work or environment setup.

Q: What makes successful candidates stand out?
They communicate clearly, seek alignment early, write idiomatic platform code, and connect technical decisions to user and business outcomes. They handle feedback gracefully and demonstrate ownership.

Q: Is the role remote or location-specific?
Availability varies by team and level. Discuss location flexibility with your recruiter early; share any constraints so the team can plan interview logistics and potential onboarding.

Other General Tips

• Confirm constraints early: Ask about language, libraries allowed, and expected complexity before coding. It prevents misalignment and wasted effort.
• Narrate your thinking: Explain assumptions, outline the approach, and reason about trade-offs as you implement. This surfaces your judgment, not just your code.
• Test as you go: Validate with representative inputs (edge cases, empty, large). Interviewers look for engineering rigor under time pressure.
• Connect to user value: Tie architecture choices to user experience (performance, reliability, accessibility). This shows product sense.
• Manage time explicitly: Break work into milestones and checkpoint with the interviewer. It demonstrates ownership and effective execution.
• Stay adaptable: If an interviewer nudges toward a particular approach, align, explain trade-offs briefly, and move forward efficiently.

Summary & Next Steps

As a Mobile Engineer, you will shape the core Poshmark experience where community and commerce meet. The work is impactful and visible: building performant features, engineering for reliability at scale, and translating product intent into delightful mobile interactions.

Focus your preparation on three areas: platform-language coding, mobile architecture (Clean Architecture, SOLID, MVVM/MVI), and runtime fundamentals (lifecycle, performance, concurrency). Reinforce with real stories that show ownership, collaboration, and user-centric decision-making. Practice in the exact language you’ll use.

You’ve got this. Approach each step with clarity, confirm expectations early, and showcase how you build high-quality mobile experiences that move metrics. For more company-specific insights and evolving interview patterns, explore additional resources on Dataford. Step in with confidence—your preparation will show.