Mid/Senior Frontend Developer

Sensor Tower; Kraków; On-site; PLN 120,000 - 150,000; Full time

Job summary

Sensor Tower is looking for a skilled Frontend Engineer to architect and deliver scalable frontend systems while mentoring junior engineers. You will shape the technical direction of our product, collaborating closely with Product Managers and Data Science teams.

The ideal candidate has 4+ years of experience, strong skills in JavaScript, TypeScript, and React, and a mindset focused on product development. Join us in a supportive and collaborative environment.

Qualifications

• 4+ years experience in software engineering focused on JavaScript and React.
• Proven ability to architect complex state management solutions.
• Experience with unit and integration tests frameworks like Jest or Playwright.

Responsibilities

• Architect and deliver scalable frontend systems.
• Lead technical decision-making for scoped features.
• Mentor junior engineers through code reviews and training.

Skills

JavaScript

TypeScript

React

Web Performance Optimization

State Management

Tools

Jest

Playwright

TanStack Query

Redux

MobX

NextJS

Job description

Overview

Sensor Tower’s digital intelligence platform provides unparalleled insight into market trends, advertising, competitor strategies, and consumer/user audiences across mobile, web, and gaming. Its insights are trusted by more than 2,500 enterprises worldwide.

Role Summary

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

Responsibilities

• Architect and deliver complex, scalable frontend systems that are simple and effective, removing unnecessary complexity from our codebase.
• Partner with Product Managers to co-author requirements and shape scope, ensuring engineering feasibility is considered during ideation.
• Lead technical decision‑making for medium‑to‑large scoped features, taking responsibility for the successful delivery of value to the customer.
• Mentor junior and mid‑level engineers through code reviews, pair programming, and quality‑first habits across the team.
• Take ownership of the frontend stack by proactively identifying bottlenecks, technical debt or systemic issues and drive 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 expertise across the full stack.

Qualifications

• 4+ years of software engineering experience with a deep specialization in modern JavaScript, TypeScript, and React.
• Proven ability to architect complex state management. Familiarity with TanStack Query, React Router, Zustand and other libraries such as Redux, MobX, NextJS is valued.
• Design systems that handle complexity without becoming complicated, prioritizing long‑term maintainability.
• Experience elevating the skills of peers through code reviews and teaching patterns and best practices.
• Competent 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: care deeply about the "why" behind every feature, view code as a tool to solve real user problems, and be comfortable pushing back on requirements to propose better solutions.

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 backend frameworks such as Ruby on Rails or Angular and databases like Clickhouse, Mongo, Postgres.
• Knowledge of AI‑driven coding tools and models, as we encourage leveraging AI to enhance coding efficiency and unlock creative potential.

EEO Statement

We are 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 let us know so we can accommodate you.

Artificial Intelligence Disclosure

We may use artificial intelligence (AI) tools to support parts of the hiring process, such as reviewing applications, analyzing resumes, or assessing responses. These tools assist our recruitment team but do not replace human judgment. Final hiring decisions are ultimately made by humans.