Paweł Kowalski

T-shaped senior software engineer with 15+ years of experience across the full stack - from pixel-perfect React frontends to distributed NestJS/Ruby/Elixir backends and AWS infrastructure. I lean toward performance problems where an optimization saves real money.

• Used cutting-edge AI tools daily for writing code, translating designs to React Native components, writing Storybook stories, and expanding the test suite
• Implementing Peer to Peer payments for 100M+ users (8M+ DAU)
• Request money feature for Klarna and non-Klarna users (NestJS) - budget: <170ms avg response time
• Allow new users to receive money before they have an account to improve user acquisition
• Send money via QR codes (Express.js, React Native) - expectation: processing 500K+ transactions weekly across 26 markets
• Phonebook synchronization in mobile apps and backend (NestJS, React Native) - supporting 80M+/month contacts being synced while respecting privacy laws and sub-3s sync time
• Gradual rollout of all the P2P features from 1% to 100%, from 1 market to 26 while keeping 99.9% SLA
• Keeping costs of owned services low while being able to scale to handle 50x the usual traffic (Black Friday, Holiday season)
• Developed microservices communicating via GraphQL, REST APIs, and Kafka in an event-driven architecture
• Deployed microservices written in TypeScript / Node.js using customized Terraform and Kubernetes

• Technologies and frameworks used
• Developed TypeScript / React application inside a Nx monorepo - maintained 85%+ test coverage
• Contributed to Ruby (on Rails) applications, large monoliths and small microservices - expectation: p95 latency >200ms
• Added Playwright Tests: E2E, Component. Expanded RSpec coverage to reduce regressions and prevent incidents
• Used DataDog, NewRelic, Sentry, SumoLogic, Kubernetes, PagerDuty to help keep everything predictable and stable
• Integrated mission-critical microservices written in Node.js using GraphQL and a distributed Kafka setup
• Adopted AI-assisted coding workflows across the team to speed up delivery
• Development and maintenance
• Reworked licensing mechanism to accommodate enterprise customers
• Rewrote frontend for Single Sign On which allowed us to serve enterprise users - handling 200K+ monthly authentications with 2FA across SAML/OAuth providers
• Implemented CSV Team and Users import functionality across 3 micro-services - expected load: 10M+ records/month
• Improved observability by adding monitors and dashboards which resulted in fewer SEV-1 incidents in our domain

• Worked with stakeholders/designers to lower user friction and improve user experience - reduced user onboarding time by 25% while maintaining accuracy in KYC and tax document validation
• Implemented Cypress parallel test runs to reduce deployment time by 50% on GitHub Actions
• Developed and maintained Elixir/Phoenix application with React (GraphQL + React Query) frontend

• Serverless & AWS optimization
• Image processing service using S3/Lambda/Sharp - scaled down EC2 instances by offloading CPU-intensive image processing to Lambda
• Unzip service with no file size limit using S3/Lambda/Streams - scaled down EC2 instances by streaming deployment files directly to S3 and processing with Lambda, eliminating background job overhead
• Reduced AWS bill by 35% by optimizing instance types for EC2, RDS, and ElastiCache, implementing S3 storage tiers, leveraging spot instances, and tuning auto-scaling policies
• Introduced GraphQL API as a replacement for deprecated REST API for external customers
• Implemented JavaScript code quality tools and tests running on GitHub Actions
• Wrote a Node.js CLI used by all clients to validate and deploy their applications
• Led implementation of E2E testing in the company and trained QA to automate their testing scenarios
• Developer advocate
• Authored articles on frontend/performance best practices to promote awareness and adoption
• Led technical development of award-winning documentation and marketing website

• Maintained application in Ruby on Rails
• Implemented capitalization table calculations using Vanilla JS - processing complex equity structures for 409A valuations

• Upgraded a legacy frontend to modern standards within 3 months while handling assigned tasks — cut page load times from 3.4s to 1.9s
• Mentored junior front-end developers
• Built custom interactive visualizations using D3.js (organization chart) and HighCharts.js

• Developed and maintained post-login banking service