Senior Fullstack Engineer

X-FLOW; Warszawa; Hybrid; PLN 180,000 - 280,000; Full time

Job summary

X-FLOW is seeking a Senior Fullstack Engineer to join our flagship project, Happy Color. You will design backend APIs in PHP/Laravel and build frontend interfaces with TypeScript/React.

You will optimize performance, define API contracts, and contribute to testing, CI, and observability. Flexible hours and remote/office options enable a creative, dynamic work environment.

Collaborate with a diverse global team and grow your skills while delivering high-quality products loved by millions.

Qualifications

• :

Responsibilities

• Design and develop RESTful APIs using PHP/Laravel.
• Build frontend applications using TypeScript/React with a focus on performance and Developer Experience (DX).
• Integrate with external services; define and maintain API contracts.
• Optimize performance, perform profiling, and reduce latency.
• Design database schemas, handle migrations, indexing, and query optimization.
• Contribute to quality assurance: write tests (unit/integration/e2e), conduct code reviews, and automate checks.
• Ensure observability and reliability: implement logs, metrics, alerts, and traces.
• Participate in designing architectural solutions.

Skills

PHP

Laravel

TypeScript

React

Redux Toolkit

REST API

PostgreSQL

MySQL

Redis

Kafka

OAuth2/JWT

DDD/SOLID

Tools

GitLab CI

Jest

Playwright

Job description

X-FLOW is a mobile game development company established in 2018. We gained recognition after the release of Happy Color, the most popular digital coloring book and one of the most successful ad-driven mobile apps in the world. We take pride in our diverse and talented team and partners, spread across the UK, Cyprus, the Netherlands, and other regions worldwide.

We are currently looking for a Senior Fullstack Engineer for our flagship project, Happy Color.

Key Responsibilities:

• Design and develop RESTful APIs using PHP/Laravel.
• Build frontend applications using TypeScript/React with a focus on performance and Developer Experience (DX).
• Integrate with external services; define and maintain API contracts.
• Optimize performance, perform profiling, and reduce latency.
• Design database schemas, handle migrations, indexing, and query optimization.
• Contribute to quality assurance: write tests (unit/integration/e2e), conduct code reviews, and automate checks.
• Ensure observability and reliability: implement logs, metrics, alerts, and traces.
• Participate in designing architectural solutions.

Requirements:

• 4+ years of experience with PHP, strong knowledge of Laravel (DI, queues, profiling, REST, modularity).
• 4+ years of experience with TypeScript, strong knowledge of React/Redux Toolkit, routing, build processes, and bundle optimization.
• Databases: PostgreSQL/MySQL, Redis; experience with schema design, indexes, and transactions.
• Message Queues/Buses: Kafka — experience with event-driven integrations.
• Security: OAuth2, JWT.
• Understanding of DDD, SOLID, 12-Factor App methodology, and observability (Prometheus/Grafana, OpenTelemetry).

Nice to have:

• Experience with Golang development.
• Development experience with Ant Design (Antd)
• 5+.Experience with or understanding of GitLab CI, feature flags, migrations, and blue-green/rolling deployment strategies.
• Testing tools: Jest, Playwright; for PHP — PHPUnit/Codeception; integration/e2e testing experience.

What We Offer:

• Competitive salary and benefits package.
• Opportunity to work with a talented and passionate team in a creative and dynamic environment.
• Flexible working hours and remote/office work options.
• Career growth and professional development opportunities.
• A fun and inclusive company culture that celebrates diversity and creativity.

Join us and let’s create great product together!