Principal C#/.NET Engineer — Mainframe Modernization Hybrid

Rulesys Technologies Inc; Hamilton, Northern (NJ, KY); Hybrid; USD 124,000 - 207,000; Full time

Benefits offered by this job

Hybrid work arrangement

Job summary

NJDHS in New Jersey seeks a Lead C#/.NET Engineer to modernize a large mainframe-derived benefits system, converting COBOL/JCL to C#, and migrating data to PostgreSQL on AWS. You will define EF Core data models, APIs, and CI/CD processes while preserving exact business logic and performance within nightly batch windows.

The role combines leadership with hands-on development, ensuring correctness, scalability, and maintainability of critical government benefits software.

Qualifications

• 12-15 years of professional C#/.NET software engineering, including senior/lead responsibilities
• Deep expertise in C# and the .NET platform (.NET Framework and .NET Core / .NET 6/8+), including async programming, memory/performance optimization, and modern language features
• Expert-level Entity Framework / EF Core: entity modeling, Fluent API, migrations, query optimization, transactions, concurrency, provider-specific behavior
• Strong relational database skills; PostgreSQL strongly preferred (Oracle/SQL Server acceptable) — schema design, indexing, query tuning, stored procedures
• ASP.NET Core Web API design (REST) for front-end integration
• Testing discipline: unit/integration regression testing frameworks; TDD/mocking
• Git, CI/CD, and static code analysis (SonarQube)
• Proven ability to read, reason about, and safely refactor large, unfamiliar codebases
• Exceptional attention to correctness — financial/benefit calculation accuracy
• Legacy modernization experience or mainframe knowledge is a plus

Responsibilities

• Refactor COBOL-derived C# into idiomatic, maintainable .NET with clean OO design
• Work in .NET Core/.NET latest; apply modern C# features (LINQ, async/await, records)
• Design and implement service layers, domain models, and APIs (ASP.NET Core Web API) for the Angular UI
• Refactor legacy batch/procedural logic into maintainable .NET; ensure correct decimal/financial arithmetic
• Optimize performance to meet nightly batch windows and SLAs

Skills

C#/.NET

EF Core

PostgreSQL

AWS

REST API

Angular

Unit tests

CI/CD

Git

TDD

Performance

Mainframe modernization

Tools

Npgsql

SQL

Job description

NJDHS in New Jersey seeks a Lead C#/.NET Engineer to modernize a large mainframe-derived benefits system, converting COBOL/JCL to C#, and migrating data to PostgreSQL on AWS. You will define EF Core data models, APIs, and CI/CD processes while preserving exact business logic and performance within nightly batch windows.

The role combines leadership with hands-on development, ensuring correctness, scalability, and maintainability of critical government benefits software.