For our client we are looking for Senior Backend DeveloperAbout the productA cloud‑based solution with a Chrome extension at its core to capture and process high‑value data from e‑commerce stores. Your mission is to design and lead the technical direction of the extension and the data pipeline, and to deliver hard, dashboard‑heavy frontends that turn raw signals into actionable insights.Join our team building the backend for a Chrome extension and data processing services in the e‑commerce/data cloud ecosystem. We are looking for a Senior Backend Developer who will lead API and data service development in Node.js and optionally take on Product Owner responsibilities for their stream.What you’ll do Design and develop APIs (REST/JSON, optionally GraphQL) for Chrome Extension: authentication, sessions, rate‑limiting, security. Build and scale data processing services (batch/near‑real‑time): ETL/ELT, validation, enrichment, normalization. Define user models (profiles, roles/permissions, audit) and implement data indexing for fast queries and reporting. Design and maintain MongoDB: schema modeling, composite indexes, replication/sharding, query optimization, monitoring. Write reliable backend code in Node.js (TypeScript preferred) with a focus on quality (tests, code review) and observability (metrics, logs, tracing). Collaborate with Frontend/QA/DevOps and business stakeholders; contribute to architecture decisions and roadmap. Optional: take on Product Owner responsibilities — discovery, backlog prioritization, release planning, and stakeholder communication. Requirements Senior level: 6+ years of commercial backend experience; strong proficiency in Node.js (Express/Fastify/NestJS). Experience designing APIs for client apps/browser extensions (Chrome). Hands-on experience with data processing (batch/stream), queues/asynchronous messaging, resilience and idempotency. Excellent knowledge of MongoDB: schema design, indexing, replica/sharding, performance tuning, backup/restore. Security and scalability: authN/authZ (JWT/OAuth/OIDC), rate‑limiting, caching, testing (unit/integration), code review. Ability to work with product roadmaps and metrics; willingness to take on PO responsibilities (a plus). Nice to Have TypeScript, Docker/Kubernetes, AWS/GCP/Azure, GraphQL, Redis/Elastic, Kafka/RabbitMQ/SQS. Knowledge of DDD/integration patterns (event‑driven), SRE/observability practices.

Experience in e‑commerce / web data / adtech (bonus).

Offer 100% remote, flexible hours, and B2B collaboration. Hourly rate up to 170 pln / h A pragmatic, senior team and a delivery‑first culture.