Senior Fullstack Engineer

CloudX

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Location: United States
Job Type: full-time
Work Format: 🌍 Remote Worldwide
Salary: $150,000 – $300,000
Posted: June 29, 2026

Job Description

About CloudX

At CloudX we’re building a new supply-side advertising platform for mobile publishers. We’re convinced that an AI-native product will significantly advance the state of the art in mobile advertising; we recently raised a $30M Series A in order to bring this dream to life. We have a long history of innovation in this space — our founding team previously built MoPub (sold to Twitter for $350M) and MAX (acquired by AppLovin). Our new platform combines real technical improvements like verifiably fair auctions with a truly AI-native product experience to give publishers unprecedented control over their ad monetization strategy.

About The Team

Our Engineering team is distributed and remote — spanning UTC-8 to UTC+6, with core working hours of roughly the US Eastern business day. We have a strong ownership culture and are heavily collaborative, relying primarily on asynchronous, written, communication for coordination. We ship daily and believe that fast CI and good test coverage is the best way to remain productive as we scale. We’re small and high trust; we optimize for rapid iteration and experimentation. Everyone has access to the latest AI tools, but rather than generating vibe-slop we use them pragmatically to build better products. We are lucky to work closely with our talented Product and Business teams to make sure we’re building the right things. It’s a true early-stage startup with lots of important work to go around.

What you'll do

We are looking for a Senior Fullstack Engineer who thinks like a Product Owner. You will work closely with our Product and Business teams to understand our customers’ painpoints, design solutions, and actually write and ship code to directly solve problems. Your key responsibilities will be:

Software Engineering: deliver a best-in-class product. Do this in a way that makes everyone on the engineering team more efficient by directly building the systems, tools, and frameworks needed to allow high-velocity iteration.
Product Ownership: work with the product team, business team, and directly with our customers to come up with new features and improvements that impact our product development roadmap.
Technical Leadership: lead by example to help develop our engineering team’s practices, particularly when it comes to testing and scaling a product whose core functionality involves large-scale, complex, sensitive, data processing.

Who you are

We encourage you to apply if you meet these requirements:

Hands-on expertise: you may have managed or led at points in your career, but you still code regularly and are interested in continuing to do so. You’ve been in charge of larger projects or initiatives and know how to work well with others.
Strong written communication skills: you are used to writing about, speaking about, and generally communicating complex technical subject matter both to other engineers and to non-engineers.
Early-stage mentality: you understand that success at a startup involves grit and determination. You have good taste when it comes to trading off speed vs. perfection. You know when to cut corners but aren’t afraid to advocate for rigor when you believe it’s necessary.
True fullstack experience: while you may be stronger on the backend or on the frontend, you are strong in either domain and have a track record of delivering projects involving both.
AI forward: you are actively experimenting with or using AI as part of your software engineering practice. You don’t send vibe-coded slop to your teammates to review, but you use AI appropriately to achieve great results.
High ownership: you care a lot about your work and when you ship a product, you make sure it continues to solve problems for the customer. You care a lot about the customer, the overall business, and are constantly trying to help achieve success — with or without code.

While not required, we’re particularly interested in candidates with:

Adtech experience: you’ve worked in adtech, particularly mobile adtech, and have a good understanding of the broader ecosystem and market.
AI product experience: you’ve built products or side projects that involve AI. You have a decent idea about what’s possible with current models and APIs, as well as a sense for what might be possible in the near future. You’ve spent time actually integrating with large foundation model APIs.
Stack experience: our backend is written in Golang, we put application state in Postgres, we store a lot of event data in Clickhouse, we use Datadog for observability. Our frontend is Typescript, React, Vite, Tailwind, Biome, ESlint. We deploy on Vercel. Familiarity with any or all of these, particularly Golang and React, is a strong positive.

In general, we’re looking for people with grit, passion, and talent. If you’re not sure if this role is an exact fit, we encourage you to apply. Many members of our team have had interesting career paths and we relish the chance to work with extraordinary individuals.

Pay and Benefits

The annual US base salary range for this role, and other engineering roles, is $150,000 – $300,000. This salary range is broad in order to accommodate a wide range of candidates; the interview process will narrow it down based on a number of factors, including your experience, qualifications, and location.

We offer equity compensation and top-tier medical, dental, and vision benefits.

We also have a generous hardware budget for a computer, monitor, and other core equipment necessary to work effectively on a remote team.

We care about the quality of your work more than the specific hours you spend getting it done, and try to minimize the number of synchronous meetings in favor of greater flexibility. There is no in-office requirement.

🎯 Who is this job for?

This role is best suited for a Senior Fullstack Engineer with strong experience in backend and frontend development, product ownership, and technical leadership in startup environments. The candidate should be proficient in Golang, React, TypeScript, PostgreSQL, scalable system design, testing, AI-assisted development, and cross-functional collaboration, with adtech and AI product experience as strong advantages. They should be familiar with building end-to-end fullstack features, designing large-scale data processing systems, working directly with customers and product teams, and balancing rapid delivery with engineering quality.

💬 Potential Interview Questions

How would you design a scalable backend service in Go to process billions of ad events while ensuring low latency and reliability?
Answer: I would build stateless Go services, use asynchronous processing where appropriate, store transactional data in PostgreSQL, analytical event data in ClickHouse, and rely on horizontal scaling, efficient indexing, and observability with Datadog.
What are the advantages of using ClickHouse instead of PostgreSQL for analytics workloads?
Answer: ClickHouse is optimized for OLAP queries, columnar storage, and high-speed aggregations over massive datasets, while PostgreSQL is better suited for transactional (OLTP) workloads and relational consistency.
How would you structure a React + TypeScript application to remain maintainable as it grows?
Answer: I would organize the project by features, use reusable components, strong TypeScript typing, custom hooks for business logic, and separate UI from data-fetching while enforcing code quality with ESLint and Biome.
How do you balance rapid feature delivery with maintaining high test coverage in an early-stage startup?
Answer: I prioritize automated tests around critical business logic and high-risk areas, keep CI fast, and focus on delivering incremental changes while preventing regressions through continuous testing.
Describe how you would optimize a slow SQL query in PostgreSQL.
Answer: I would analyze the execution plan using EXPLAIN ANALYZE, identify bottlenecks, add or adjust indexes, rewrite inefficient joins or subqueries, and validate improvements with real workload metrics.
How would you design a REST or GraphQL API that supports a modern React frontend?
Answer: I would create clear resource boundaries, maintain versioning or schema evolution, validate inputs, provide consistent error handling, and optimize payloads to minimize unnecessary network requests.
What role does observability play in distributed systems, and how would you use Datadog effectively?
Answer: Observability enables rapid detection and diagnosis of production issues. I would instrument services with metrics, structured logs, distributed tracing, dashboards, and actionable alerts to reduce mean time to resolution.
How have you incorporated AI tools into your software engineering workflow without compromising code quality?
Answer: I use AI to accelerate implementation, documentation, testing, and code reviews, but I always validate generated code, ensure it follows project standards, and review it with the same rigor as manually written code.
How would you build a feature that processes sensitive customer data while ensuring security and compliance?
Answer: I would follow the principle of least privilege, encrypt data in transit and at rest, validate all inputs, implement auditing where needed, and minimize exposure of sensitive information throughout the system.
Describe a project where you demonstrated product ownership rather than simply implementing requirements.
Answer: I collaborated closely with stakeholders to understand user pain points, proposed improvements beyond the initial requirements, delivered the solution end-to-end, monitored its production impact, and iterated based on customer feedback and business metrics.

📋 Job Summary

CloudX is an early-stage, AI-native adtech startup founded by the team behind MoPub and MAX, building a next-generation mobile advertising platform backed by a $30M Series A. As a Senior Fullstack Engineer, you'll own product features end-to-end, collaborate closely with Product and Business teams, and build scalable systems using Go, React, TypeScript, PostgreSQL, ClickHouse, Vercel, and modern AI tools. This is a fully remote global role with a strong engineering culture focused on ownership, rapid iteration, and high-quality software, offering a US salary range of $150,000–$300,000 plus equity and excellent benefits. If you enjoy solving impactful technical challenges, influencing product direction, and thriving in a high-trust startup environment, this is an outstanding opportunity to make a significant impact.