Senior Node.js Backend Engineer (Contract)

At Blazity, we are a team of React.js and Next.js experts focused on creating API-first products. We build long-term partnerships with our clients, serving as their trusted development partners. Our work involves optimizing apps, stores, and websites, implementing new features, and automating workflows to deliver outstanding results.

This is a fixed-term contract, 4-6 weeks, ~40 h/week, start ASAP

You’ll build a production-grade connector service between two SaaS APIs using our Node.js + TypeScript + Fastify service template. The template provides Fastify app scaffolding, type-safe config, dependency injection with Awilix and a custom wrapper, OpenTelemetry tracing/metrics hooks, OpenAPI (Swagger) docs site, Docker/Docker Compose, and a Vitest testing setup.

Salary ranges

B2B: 125 - 150 PLN/h

Location

100% remote from Poland 

Our requirements

• 5+ years building production services in Node.js + TypeScript; comfort with Fastify or similar frameworks.

• SaaS integrations: designing connectors/plugins between APIs (auth, data mapping, pagination, rate limits, idempotency, webhooks).

• Webhooks security: implementing HMAC verification against raw request bodies and timestamps.

• Quality & Ops: GitHub flow/PR reviews, CI; automated tests with Vitest (unit/integration/e2e with Fastify inject).

• Observability: practical use of OpenTelemetry traces/metrics and structured JSON logging.

• Data & privacy: careful handling of PII (redaction/masking in logs, scoped access).

• Documentation: clear runbooks and lightweight user guides.

Nice to have 

• Familiarity with the two target APIs’ objects/events and i18n/translation pipelines.

• Experience deploying containerized services to a managed platform.

Scope of responsibilities

• Implement auth flows (OAuth2/API key), token storage/refresh, least-privilege scopes.

• Build type-safe mappers between API models; validate requests/responses with schema guards.

• Implement webhook ingestion with HMAC-SHA256 signature verification and replay protection.

• Ensure idempotency and safe retries for outbound calls (exponential backoff + jitter; respect Retry-After; handle 429/5xx).

• Add observability: request/correlation IDs, traces, and key business metrics (events processed, retries, dedupes).

• Ship tests (unit/integration/e2e using Vitest and Fastify’s inject) and harden error handling.

• Produce handover: runbook, env/setup steps, API mapping spec, and error taxonomy.

What Makes Us Special?

📈 Our team has a genuine impact on the company’s decisions and direction.

✨ No bureaucracy – we keep things simple and efficient.

🗺️ Remote work from Poland

⏳ Flexible working hours – fit your schedule to your life.

🍕 Fun social events to connect with your teammates.

🤝 We value feedback and foster an open, supportive environment.