Senior Fullstack Engineer

X-FLOW; Warszawa; Hybrid; PLN 180,000 - 270,000; Full time

Benefits offered by this job

Competitive salary

Flexible hours

Career growth

Inclusive culture

Job summary

X-FLOW in Warsaw, Poland is seeking a Senior Fullstack Engineer to join our flagship Happy Color project. You will design and implement RESTful APIs with PHP/Laravel and build performant frontends using TypeScript and React, focusing on DX and scalable architectures.

You’ll work with PostgreSQL/MySQL, Redis, Kafka, and modern observability tools; participate in code reviews, testing, and deployment strategies, with flexible hours and hybrid work options.

Qualifications

• 4+ years of PHP experience with Laravel (DI, queues, profiling, REST, modularity).
• 4+ years of TypeScript with React/Redux Toolkit, routing, build processes, and bundle optimization.
• Database design with PostgreSQL/MySQL; Redis; indexes and transactions.
• Experience with Kafka and event-driven integrations.
• Security: OAuth2 and JWT.
• Knowledge of DDD, SOLID, 12-Factor App and observability tools.

Responsibilities

• Design and develop RESTful APIs using PHP/Laravel.
• Build frontend apps with TypeScript/React focused on DX and performance.
• Define and maintain API contracts and integrate with external services.
• Profile, optimize performance and reduce latency.
• Design database schemas, handle migrations and indexing.
• Write tests (unit/integration/e2e) and conduct code reviews.
• Ensure observability: logs, metrics, alerts, traces.

Skills

PHP Laravel

TypeScript React

PostgreSQL MySQL Redis

Kafka

OAuth2 JWT

DDD SOLID 12-Factor

Observability (Prometheus Grafana Open

Tools

GitLab CI

Jest

Playwright

JUnit/Codeception

Ant Design

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 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!