Mid/Senior Frontend Developer

Sensor Tower; Warszawa; On-site; PLN 183,553 - 256,974; Full time

Job summary

Sensor Tower is seeking a Frontend Engineer to build and define features that enhance user experience. In this role, you will take ownership of major technical components and lead the development of scalable applications, mentoring fellow engineers and driving best practices in React and TypeScript.

The ideal candidate will have over 4 years of experience, a deep understanding of state management, and a passion for creating intuitive user experiences. You'll collaborate with product managers, backend engineers, and data scientists to deliver robust solutions.

Qualifications

• 4+ years of software engineering experience with modern JavaScript, TypeScript, and React.
• Ability to architect complex state management systems.
• Experience in writing unit and integration tests using frameworks like Jest or Playwright.

Responsibilities

• Architect and deliver complex, scalable frontend systems.
• Lead technical decision-making for medium‑to‑large scoped features.
• Mentor junior and mid-level engineers through code reviews and pairing.

Skills

JavaScript

TypeScript

React

Web performance optimization

Unit and integration testing

Job description

Role Summary

As a Frontend Engineer at Sensor Tower, you will not only build features, you will define how we build them. You will take ownership of major technical components, ensuring our applications are scalable, maintainable, and fast. In our lean and flat organization, your voice will shape the technical direction of our product, helping us deliver an intuitive, fluid user experience that helps our customers understand the digital ecosystem.

Fulfill your potential with us

• Architect and deliver complex, scalable frontend systems that are simple and effective, removing unnecessary complexity from our codebase.
• You will partner with Product Managers to co-author requirements and shape the scope, ensuring engineering feasibility is considered during ideation, not just execution.
• Lead technical decision‑making for medium‑to‑large scoped features, taking responsibility for the successful delivery of value to the customer, not just the completion of tickets.
• Mentor junior and mid‑level engineers through code reviews, pair programming, and by instilling quality‑first habits across the team.
• Take ownership of the frontend stack by proactively identifying bottlenecks, technical debt, or systemic issues and driving the initiatives to fix them.
• Advocate for and drive best practices in React, TypeScript, and web performance optimization across the engineering organization.
• Collaborate deeply with Data Science and Backend Engineers to ensure seamless data flow and end‑to‑end system reliability, and use these partnerships to progressively expand your expertise across the full stack.

What we are interested in

• 4+ years of software engineering experience with a deep specialization in modern JavaScript, TypeScript, and React.
• Proven ability to architect complex state management. While our stack relies on TanStack Query, React Router and Zustand, we value engineers who understand the principles and can adapt expertise from other libraries like Redux, MobX, NextJS.
• You can design systems that handle complexity without becoming complicated, prioritizing long‑term maintainability.
• Experience elevating the skills of peers. You don't just review their code; you teach patterns and best practices.
• Competence in writing robust and efficient unit and integration tests using frameworks like Jest or Playwright.
• Deep understanding of web performance, browser internals, and optimization techniques for data‑heavy applications.
• A "Product Owner" mindset. You care deeply about the "why" behind every feature, viewing code as a tool to solve real user problems. You are comfortable pushing back on requirements and proposing alternative solutions that drive better business outcomes and user experiences.

Extra Credit

• Experience in data visualization and analytics (handling large datasets, heavy DOM manipulation with libraries like Highcharts).
• A portfolio, GitHub history, or technical writing that demonstrates clean code, an eye for design, and the ability to solve complex architectural challenges.
• Familiarity with back‑end frameworks Ruby on Rails/Angular and different types of DBs (Clickhouse, Mongo, Postgres).
• Knowledge of AI‑driven coding tools and models as we encourage leveraging AI to enhance coding efficiency and unlock creative potential.

About Sensor Tower

Sensor Tower’s digital intelligence platform provides unparalleled insight into market trends, advertising, competitor’s strategies, and consumer/user audience across mobile, web, and gaming. Trusted by more than 2,500 enterprises worldwide, our solutions empower companies to understand consumer behavior and market performance across digital platforms.

Equal Employment Opportunity

Sensor Tower is committed to equal employment opportunities regardless of race, color, ancestry, religion, sex, national origin, sexual orientation, age, citizenship, marital status, disability, gender identity, and veteran status. We will consider qualified applicants with arrest and conviction records. If you have a disability or special need, please do not hesitate to let us know and we’ll do our best to accommodate.