Middle+/Senior Full-stack Developer (Node.js, backend-focused) | Brainer

We are currently looking for a Middle+/Senior Full-stack Developer to join our project Brainer, which is building a comprehensive online platform for measuring, training, and systematically developing human cognitive abilities.

Brainer is a digital space for those who want to think faster, deeper, and more effectively. It brings together:

• brain quizzes;
• brain games;
• puzzles;
• courses and educational modules.

What will be in your focus:

• Work approximately in a 70% backend / 30% frontend ratio.
• Take significant ownership of the product’s backend development and independently handle related frontend tasks.
• Design and develop core server-side logic, including users, authorization, access management, products, reports, and other product modules.
• Evolve the architecture with regard to the growth of users, traffic, data, and integrations.
• Ensure the reliability of payment logic and correct handling of repeated requests, errors, and edge cases.
• Design and optimize database operations, identify bottlenecks, and improve system performance.
• Develop the product’s event-driven and analytics components to ensure that Product and Marketing teams receive accurate and reliable data.
• Independently implement product scenarios on the frontend in integration with APIs.
• Collaborate with the Product team on technical solutions by assessing risks and complexity and suggesting ways to validate product hypotheses.
• Improve the product’s engineering quality through code reviews, monitoring, security, integration quality, and systematic technical debt management.
• Participate in architectural decisions that will shape the product’s development over the next 1–2 years.

You are our perfect match if:

• 3+ years of commercial backend development experience with Node.js and practical experience with NestJS.
• Strong knowledge of JavaScript and TypeScript.
• Good understanding of fundamental programming and software design principles, SOLID, and GRASP, with the ability to apply them in practice.
• Practical experience with relational databases, preferably PostgreSQL, including schema design, indexes, transactions, and query optimization.
• Experience designing and developing REST APIs, authorization, JWT, sessions, cookies, and secure handling of user data.
• Understanding of reliable server-side systems, including error handling, retries, concurrent operations, scaling, and bottleneck identification.
• Practical experience with React and Next.js, sufficient to independently implement the frontend part of product scenarios.
• Understanding of product analytics and experience integrating third-party services.
• Experience using AI tools in development, with mandatory verification and understanding of the generated code.

Will be a plus:

• Experience working with high traffic, a significant number of users, or high-load systems.
• Experience with payments, subscriptions, billing, and recurring payments.
• Practical experience with caching, queues, and background task processing.
• Experience integrating AI APIs or developing generative AI-based functionality.
• Experience with CI/CD, Docker, monitoring, or cloud infrastructure.
• Experience launching a web product or a significant part of it from scratch.
• Experience working with B2C products with a high volume of paid traffic.

The stages you’ll go through:

• Stage 1. Pre-screen.
• Stage 2. Technical interview.
• Stage 3. Test task
• Stage 4. Bar interview.
• Stage 5. Reference checks.
• Stage 6. Job Offer!

For comfortable work, we offer:

• Support for your self-realization and career growth: both vertical and horizontal development, opportunities to work across different niches, and compensation for external courses and conferences.
• Flexible working hours (you can start your workday anytime between 8:00 and 11:00 AM Kyiv time).
• An office in Kyiv, coworking spaces in Lviv or Warsaw, or the option to work remotely — the choice is yours.
• 28 working days of paid vacation per year, up to 30 days of sick leave with medical confirmation, plus all public holidays observed.
• Care for your health: medical insurance, a Mental Health program, and compensation for therapy sessions.
• Ukrainian Victory Support program and other meaningful social initiatives.
• Gifts for special occasions in your life and career.
• Quarterly team buildings (online or offline).
• Equipment compensation during blackouts.
• Maximum support in challenging life situations.

If you’re driven by the challenge of building outstanding products, send us your CV — let’s get to know each other!