Senior Back End Developer (C#)

Access Softek

Poland

Remote

PLN 180,000 - 280,000

Full time

14 days+

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Benefits offered by this job

Flexible working hours

Competitive salary

Paid vacation and holidays

Medical insurance policy

Mental health coverage

Training compensation

Equipment provided

Internet allowance

Job summary

Access Softek is seeking a Senior Back End Developer (C#) to join our Banking Platform Team. You will work on core services behind our online banking platform used by hundreds of FI clients, migrating from monolith to microservices and solving high-scale backend challenges. Expect overlap with 2 AM–10 AM PST/PDT; strong engineering and cloud architecture exposure are core.

Collaborative, distributed team. You will work with C# .NET Core, .NET Framework 4.8, MS SQL Server, RabbitMQ, and REST,

Qualifications

5+ years building web apps/backend APIs in C#.
Experience making architectural decisions and owning technical trade-offs.
Strong OOD principles, classic design patterns (GoF).
Experience with microservices architecture, as well as working with and modernizing legacy systems.
Strong data modeling / MS SQL / data access optimization.
Experience with API design, implementation, and troubleshooting.
Unit & integration testing (NUnit/xUnit, FluentAssertions, Moq).
Comfortable owning code from commit to production, with strong CI/CD and Git-based workflow experience.
Understanding of web security fundamentals and secure coding practices.
Comfortable using AI tools as a core part of daily engineering work — applied to production-quality code, not just casual experimentation.
Experience integrating LLM/AI features into products (agents, RAG, MCP-based tooling).
Good communication skills and Intermediate+ English.

Responsibilities

Lead design and delivery of complex features, from ideation to production.
Proactively identify problems and drive technical decisions with minimal oversight.
Use AI-assisted tools to accelerate delivery, critically validating output for correctness and security.
Produce clear documentation for API consumers.
Drive automated test coverage for your components.
Own and evolve code within your product area, including microservices architecture.
Modernize legacy functionality and improve the maintainability of existing solutions.
Follow engineering best practices around code review, version control, CI/CD, and secure development.
Investigate issues, analyze logs and telemetry, and deliver safe, reliable fixes.
Share knowledge and help improve team development practices.

Skills

C# backend

Architecture decisions

OOD design patterns

Microservices

MS SQL data modeling

API design

Unit/integration tests

CI/CD

Secure coding

AI tooling

English communication

Tools

RabbitMQ

REST

GitHub Copilot

Cursor

Claude Code

ChatGPT

MS SQL Server

Job description

Access Softek has been building software for the financial industry for over 30 years. Headquartered in Berkeley, California, we work with hundreds of banks and credit unions across the U.S., helping them deliver modern digital banking experiences to millions of users.

We are looking for a Senior Back End Developer (C#) to join our Banking Platform Team.

This team builds and maintains the core services behind our award-winning online banking platform, used by 400+ Financial Institution clients. Their work includes leading complex feature delivery and driving our monolith-to-microservices migration — the kind of work that combines deep backend engineering with real-world FinTech and cloud architecture challenges. The team is a strong fit for an engineer who enjoys solving complex, high-scale backend problems and wants to gain deep exposure to cloud architecture in a mission-critical domain.

You will work with C# .NET Core, .NET Framework 4.8, MS SQL Server, RabbitMQ, and REST, partnering closely with product managers, QA engineers, and front-end developers in a distributed team. AI-assisted development tools (GitHub Copilot, Cursor, Claude Code, ChatGPT) are also part of the team's everyday workflow, helping developers move faster with coding, debugging, refactoring, testing, and documentation.

Important: this role requires overlap with 2 AM–10 AM PST/PDT — some flexibility is possible in both directions.

Primary Responsibilities:

Lead design and delivery of complex features, from ideation to production.
Proactively identify problems and drive technical decisions with minimal oversight.
Use AI-assisted tools to accelerate delivery, critically validating output for correctness and security.
Produce clear documentation for API consumers.
Drive automated test coverage for your components.
Own and evolve code within your product area, including microservices architecture.
Modernize legacy functionality and improve the maintainability of existing solutions.
Follow engineering best practices around code review, version control, CI/CD, and secure development.
Investigate issues, analyze logs and telemetry, and deliver safe, reliable fixes. li>
Share knowledge and help improve team development practices.

Requirements:

5+ years building web apps/backend APIs in C#.
Proven experience making architectural decisions and owning technical trade-offs.
Strong OOD principles, classic design patterns (GoF).
Experience with microservices architecture, as well as working with and modernizing legacy systems.
Strong data modeling / MS SQL / data access optimization.
Experience with API design, implementation, and troubleshooting.
Unit & integration testing (NUnit/xUnit, FluentAssertions, Moq).
Comfortable owning code from commit to production, with strong CI/CD and Git-based workflow experience.
Understanding of web security fundamentals and secure coding practices.
Comfortable using AI tools as a core part of daily engineering work — applied to production-quality code, not just casual experimentation.
Experience integrating LLM/AI features into products (agents, RAG, MCP-based tooling), building internal AI-driven developer-productivity tooling would be a plus.
Good communication skills and Intermediate+ English.

What We're Looking For (Beyond Tech Skills):

Communication & Clarity — Explains problems, trade-offs, and solutions clearly to both technical and non-technical stakeholders.
Ownership & Accountability — Takes accountability for outcomes, proactively flags risks, and stays engaged beyond assigned tasks.
Growth Mindset & Leadership — Eager to learn, goal-oriented, with experience leading a team, project, or initiative.

Our benefits: