.NET Backend Engineer

0to9 Ab; Wrocław; Hybrid; PLN 200,000 - 280,000; Full time

Job summary

0TO9 is building fintech platforms and seeks a backend-focused engineer to help shape scalable systems using C# and .NET on AWS ECS.

You will own services end-to-end, apply DDD and CQRS, ensure reliability, observability, and security, with the potential to contribute to frontend features in TypeScript/React/Vue.

Qualifications

• Backend engineering with C#/.NET in distributed systems.
• Experience with AWS and microservices.
• Familiarity with DDD and CQRS concepts.

Responsibilities

• Build and maintain C#/.NET microservices on AWS ECS.
• Collaborate with product managers, architects, and engineers to deliver high-performance APIs.
• Write clean, testable code following SOLID principles.
• Apply DDD and CQRS to create modular, scalable systems.
• Design event-driven communication using NATS.
• Ensure reliability through idempotency, retries, and self-healing services.
• Implement observability: logging, metrics, tracing, and performance monitoring.
• Work with Relational (MS SQL Server) and NoSQL (DynamoDB) databases.
• Contribute to secure design (auth, secrets, compliance).
• Improve CI/CD, containerized workflows, and engineering practices.
• Optionally, frontend work (TypeScript, React or Vue) when end-to-end ownership is needed.

Skills

C#

.NET

AWS

Microservices

DDD

CQRS

Event-driven

CI/CD

Testing

Clean code

Tools

AWS ECS

S3

IAM

Datadog

Secrets Manager

KMS

GitHub Actions

Job description

About 0TO9

0TO9 is a bank for entrepreneurship, built by and for financial innovators. We provide infrastructure for entrepreneurs ready to start and scale the next generation of financial products and platforms. Founded in Stockholm in 2025, we're already 200+ co-workers across Europe, with offices in Stockholm and Berlin.

Our name reflects our mission: from zero to success, from idea to impact, from now to what's next.

About the role

At 0TO9 you'll build the systems behind the next wave of fintech ventures. It's a chance to solve complex problems at scale, on systems that are still young enough to shape.

• Build and maintain C#/.NET microservices on AWS ECS.
• Collaborate with product managers, architects, and engineers to deliver high-performance APIs
• Write clean, testable code following SOLID principles.
• Apply DDD and CQRS to create modular, scalable, and maintainable systems.
• Design event-driven communication using NATS.
• Ensure reliability through idempotency, retries, and self-healing services.
• Implement observability: logging, metrics, tracing, and performance monitoring.
• Work with both relational (MS SQL Server) and NoSQL (DynamoDB) databases.
• Contribute to secure design (auth, secrets, compliance).
• Improve CI/CD, containerized workflows, and engineering practices.
• Optionally, follow a feature into the frontend (TypeScript, React or Vue) when it needs to land end to end.

How we build

Agentic coding is our default, not an experiment. Across the group, we run a Claude-Code-native workspace:

• Engineering standards loaded as a skill, so agents apply them automatically.
• A git-backed knowledge base that agents read and extend.
• Agent workflows that take a change from branch to reviewed PR.
• An automated reviewer in CI that counts as an approving review on a pull request.

We're looking for someone who already works this way, and is comfortable making agents a normal part of how they build.

About you

We think you'll be a great fit if you:

• Have backend experience working with microservices and distributed systems, C# and .NET, and AWS.
• Take ownership, challenge unclear requirements, and prioritize reliability.
• Have applied DDD and CQRS in real-world systems.
• Understand event-driven architectures (ideally with NATS).
• Care about writing clean, maintainable, testable code.
• Already lean on LLMs and agentic tools daily, you see them as leverage, not a shortcut.

Technical Requirements

We build on .NET and SQL on the backend, with TypeScript, React and Vue, on the frontend. This role lives on the backend, and C# is a requirement. Frontend is a bonus, not a bar.

Cloud & Infrastructure

• AWS-native: ECS/Fargate, S3, least-privilege IAM.
• Container fluency: build, ship, and debug in production.
• Security by default: WAF, encryption at rest and in transit.
• EU data residency: aware of why region matters.

Architecture

• Microservices & DDD: boundaries by domain, not layer.
• API/event-driven: no shared databases.
• Resilience patterns: retries, backoff, idempotency.
• Clean, SOLID code: safe for a human or an agent to extend.

Delivery & Quality

• CI/CD fluency: GitHub Actions or equivalent.
• Test-driven habits: 80%+ coverage, no exceptions.
• Reviewable PRs: small diffs, no self-merges.
• Supply-chain hygiene: dependency & SCA scanning before ship.

Observability & Security

• Structured logging & tracing: CloudWatch, Datadog, or equivalent.
• Zero hardcoded secrets: Secrets Manager or equivalent, always.
• Encryption everywhere: KMS at rest, TLS in transit.

Nice to have

• Previous fintech or banking industry experience, you'll ramp faster.
• Hands-on experience with integration testing, contract testing, or end-to-end service testing.
• Knowledge of observability tools and testing strategies for microservices.
• Understanding of cloud security, governance, and compliance.
• Frontend comfort in TypeScript, React or Vue. Not required, but it's how you end up owning a feature end to end rather than half of one.

Find out more at 0to9.com — we'd love to hear from you.