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Sergey Filippov

@sergeyfilippov

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Senior full-stack engineer (Ruby on Rails & React) focused on product outcomes.

Argentina

Message

What I'm looking for

I seek mid/senior roles in established teams where I can drive pragmatic product-focused engineering, own architecture and payments, mentor engineers, and build reliable, tested systems with room for AI-assisted automation.

I am a senior full-stack engineer specializing in Ruby on Rails and React/Hotwire, with over 5 years delivering production-grade SaaS systems across EdTech and FoodTech. I co-founded a boutique agency and led a small engineering team while owning technical delivery and architecture.

I've designed and implemented backend systems for student management, billing, scheduling, and large-scale CSV exports, and built resilient payment workflows using Direct Debit and Stripe that improved debt recovery from ~10% to ~90%.

My work emphasizes pragmatic, product-focused execution: implementing hierarchical RBAC with JSONB and Pundit, stabilizing exports with batched Sidekiq jobs, and reducing operations overhead by 3–8 hours/week with Turbo workflows. I also design AI-assisted automations with RAG/tool-use flows and strong guardrails.

I prioritize testing, CI, documentation, and mentoring—driving RSpec test coverage, GitHub Actions pipelines, and onboarding processes—while seeking mid/senior roles within established teams where I can contribute architectural leadership and hands-on development.

Experience

Work history, roles, and key accomplishments

Current

Senior Full-Stack Engineer

Current

FJ Tech

Aug 2020 - Present (5 years 4 months)

Co‑founded and led engineering for a boutique agency delivering production-grade Rails + React/Hotwire SaaS systems; designed architecture, billing workflows, RBAC, and CI, improving debt recovery from ~10% to ~90% and eliminating CSV timeouts.

Ruby on Rails React Hotwire (Turbo + Stimulus)Sidekiq PostgreSQL Stripe AWS S3

Full-Stack Engineer (FoodTech)

FJ Tech

May 2021 - May 2023 (2 years)

Built V1 backend for a sustainable food delivery WeChat Mini Program serving ~135k users and 400 restaurants, implementing order lifecycle, courier integration, promotions, and operational tooling to keep the platform in production.

Rails API JWT Background Jobs PostgreSQL

Instructor

Le Wagon

Oct 2020 - Aug 2022 (1 year 10 months)

Taught full-stack web development (Ruby on Rails, JS, SQL, Git) and guided students through MVC, relational modeling, and collaborative Git workflows to accelerate practical developer skills.

Ruby on Rails JavaScript SQL Git MVC Debugging