Senior Python Backend Engineer (Part-time, 2 days/week) Code Review & Platform Stability w Warszawa, Polska

Expected, Python, FastAPI, Django, Docker, Git, REST API, PostgreSQL, CI/CD, CI

Optional, Stripe, Meta API, Amazon Ads API, Redis, Celery, GDPR, AWS

About the project, We're looking for a senior backend engineer to be the technical safety net of our platform, 2 days per week. You won't be building most features. Your job is to review what we ship, catch problems early and keep the application stable as we grow.

Your responsibilities, Review backend code and architecture decisions written by our team and AI coding agents, and give clear, prioritized feedback, Identify bugs, security vulnerabilities, performance bottlenecks and technical debt, and fix critical issues yourself when needed, Keep our many third-party API integrations reliable (Meta, Amazon, Stripe and others): error handling, retries, rate limits, token refresh, webhooks, Improve observability: logging, monitoring and alerting, so we catch problems before our users do, Define and enforce backend standards for testing, code structure, migrations and deployments, Advise on hardening the platform for production as we scale: payments, user data, growing traffic, Mentor our fullstack developers through reviews and short technical discussions

5+ years of commercial backend development in Python, Strong hands-on experience with FastAPI and/or Django, Proven track record of building and maintaining third-party API integrations: OAuth flows, webhooks, rate limits, retries, async/background jobs, Solid PostgreSQL skills: data modeling, migrations, query performance, Experience running production systems: CI/CD, monitoring, logging, incident handling, Security mindset: authentication, secrets management, handling personal data under GDPR, Experience doing thorough code reviews, and the ability to critically review AI-generated code, Clear written communication: you can explain what's wrong, why it matters, and how to fix it

What we offer, Part-time: 2 days per week, fully remote, flexible days, B2B contract, Real ownership over the technical quality of a growing product, A small team where your feedback directly shapes how we build, Direct work with the founder, with no corporate layers

About Us, Deeplytrees is building Lens, a creator-marketing platform that helps brands run influencer campaigns end to end. It covers creator discovery, content compliance checks, sales attribution, ad campaigns and creator payouts. The platform relies on many API integrations (Meta, Amazon, Stripe and more), and much of our code is written with AI coding agents while our team owns the architecture and testing.