Michał Krzyżanowski

@krzyzak
Principal Engineer Ruby & Rails 15+ yrs
 * From architecting MVPs as a sole developer
 * to Principal Engineer across a 200+ engineer organisation at Toptal.
 * Mostly fintech, travel, carbon markets, and SaaS — though happy to work on new domains.

open source

stack

Ruby Rails AI/LLMs PostgreSQL Hotwire JavaScript/TypeScript APIs GraphQL React SQL NoSQL + whatever it takes

can help with

System Architecture
Design scalable, maintainable systems — from greenfield builds to legacy rewrites. Multi-tenant SaaS, high-throughput APIs, PostGIS-backed geo systems handling millions of users.
Backend Engineering
Hands-on backend development in Ruby and Rails. API design, data modelling, background processing, third-party integrations — reliable, well-tested, production-ready code.
Fractional CTO
Strategic technical leadership without the full-time cost. I help early-stage companies make the right architectural bets, set up CI/CD & culture, and avoid the classic mistakes that slow down scale.
Technical Strategy
Bridge the gap between business objectives and engineering execution. Translate complex product requirements into clear technical roadmaps and help stakeholders make confident decisions.
MVP Development
Ship fast, learn faster. I've built production-ready MVPs solo — from database schema to deployment — and know how to prioritise ruthlessly to get something real in front of users quickly.
Performance Scaling
Diagnose where bottlenecks actually are — slow queries, missing indexes, N+1s, cache misses — and fix them. I can meaningfully improve the performance of critical paths in existing Rails applications.
Code Review & Mentoring
Raise the bar across your team. I embed quality standards through thoughtful review, pairing, and async feedback — resulting in codebases that are easier to test, change, and understand.
API Design
Build clean, versioned, well-documented APIs. Whether REST or GraphQL, I design contracts that frontend teams love and that stay maintainable as requirements evolve.
Hire me — send email
Michał Krzyżanowski
Available for remote positions only

selected experience

Promoted to the first Principal Engineer in Toptal’s history, leading technical strategy across a 200+ engineering organisation — the world’s largest fully-remote freelance talent network. Spearheaded company-wide technical initiatives and mentored senior engineers across multiple product teams.

Led a complete rewrite of the sanctions-checking system to handle 300% traffic growth and evolving fintech compliance requirements. Conducted risk assessment, translated complex regulatory needs into technical specs, and managed end-to-end delivery including stakeholder communication and cross-team coordination.

Developed cutting-edge backend systems for an EU ETS (Emission Trading System) quota management platform serving enterprise clients in the carbon trading market. Built high-performance data pipelines and API integrations handling complex regulatory compliance and real-time market data.

Built a robust data integration platform processing travel information from 50+ diverse partner APIs for the world’s leading travel guide company. Implemented aggregation, sanitisation, and normalisation systems handling millions of data points.

get in touch

michal.krzyzanowski@gmail.com