Senior .NET Modernization Engineer

What You'll Do6

• Read the existing codebase to establish what the system actually does, then draw out hidden behavior and edge cases by questioning the domain experts directly.
• Slice the upgrade into small, safe, releasable steps, decide which parts stay exactly as they are, and spell out the trade-offs in plain language.
• Write and review production code every day, directing AI coding agents with judgment instead of raw speed.
• Build the regression safety net as the migration moves: characterization tests plus replays of production-like data through old and new versions so outputs can be compared, since a wrong number means someone gets paid incorrectly.
• Push each change to production with a rollback plan ready for that step.
• Surface risks early and keep engineers, product, and leadership current on where things stand.

Requirements6

• Roughly 8-10+ years of professional C#/.NET work, with real depth in .NET Framework 4.x.
• Hands-on leadership or a major share of a .NET Framework to modern .NET migration on a large system that stayed live in production throughout. A greenfield rewrite or a small app port does not count.
• Solid MongoDB background, including work through driver and server version upgrades.
• Comfort in large legacy codebases with thin test coverage, and the habit of adding regression safety before changing behavior.
• Uses AI coding tools such as Claude Code, Cursor, or Copilot every day, and backs their output with tests, review, and evidence.
• Clear communicator who can gather requirements on their own inside a product team and explain technical risk to non-engineers.

Preferred Qualifications5

• .NET Standard 2.0 and multi-targeting for shared libraries during incremental migrations.
• HR tech, benefits, payroll, leave and absence, or another rules-heavy business domain.
• Multi-tenant SaaS work with per-customer data isolation.
• AWS, Docker, CI/CD through GitHub Actions or Jenkins, and observability such as Datadog.
• A second modern stack, for example TypeScript or Node.js.

Who Should Apply

Engineers who have already carried a large legacy .NET system through an in-place modernization, and who treat MongoDB driver upgrades as familiar ground, fit this best. Devblock wants someone who reads old architecture firsthand and aims AI agents with precision. Curiosity about leave and absence rules matters more than prior HR tech experience.

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