Senior .NET Modernization Engineer (Remote - USA)

Braintrust; United States; Remote; USD 138,000 - 165,000; Full time

Job summary

Devblock is seeking a Senior .NET Modernization Engineer for a remote engagement in the United States. You will lead migration from .NET Framework to modern .NET, work with MongoDB driver/server upgrades, and apply AI-assisted coding responsibly within a production context.

The role emphasizes deep architectural reasoning, end-to-end ownership, and collaboration with product and leadership to deliver safe, incremental upgrades and reliable releases.

Qualifications

• 8–10+ years of professional C#/.NET experience.
• Deep expertise in .NET Framework 4.x and legacy ASP.NET.
• Proven MongoDB experience with driver/server upgrades.
• Experience migrating large systems while in production.
• Daily use of AI coding tools with tests and evidence.
• Strong independent communicator within a product team.

Responsibilities

• Analyze legacy code and plan migration steps end-to-end.
• Write and review production C#/.NET code with AI tools.
• Design tests and characterize outputs to verify changes.
• Coordinate releases with rollback plans.
• Collaborate with product, engineering, and leadership.

Skills

C#/.NET

MongoDB

AI coding tools

Strong communicator

Legacy code

Tools

Claude Code

Cursor

Copilot

GitHub Actions

Job description

• Rate: $100 – $120/hr
• Hours: 40 hours / week
• Experience: 10+ years
• Location: New York, NY, USA + 1 more

Help bring a decade-old production system onto modern .NET and MongoDB without breaking what employers and their employees rely on every day. This is a role for an engineer whose judgment matters more than their typing speed, working AI-first alongside a team that already does.

Contract, 3+ months, likely extending, Remote, US time zones preferred, Forward-deployed, hands-on

About the Project

We're modernizing the core of an established HR technology SaaS platform that employers use to manage employee leave, absence, and pay. It's a decade-old .NET monolith built around a rich domain model, it runs in production every day, and it has limited automated regression coverage. That makes the work fragile and complicated, and it's why we need more than a strong engineer.

The upgrade path:

• .NET Framework 4.8 to .NET Standard to .NET 10
• MongoDB 6 to 7 to 8

What We Need

We need someone who knows how the old stuff works: legacy .NET Framework, older ASP.NET patterns, and earlier MongoDB drivers. You should also work in a modern, AI-forward way. Being fast at prompting doesn't qualify you here. You need deep coding experience, enough to reason through old code and architecture yourself, direct AI tools with precision, and catch the AI when it's confidently wrong.

This is also a forward-deployed role, not a ticket queue. You'll work directly with the product team's engineers and domain experts and own the work end to end:

• Requirements and discovery: work out what the system is supposed to do, often from the code itself, and ask the questions that surface hidden behavior and edge cases.
• Architecture and migration planning: sequence the upgrade into small, safe, releasable steps, decide what to keep exactly as-is and what to rethink, and make the trade-offs clear.
• Hands-on coding: write and review production code every day, using AI coding agents heavily and with judgment.
• Testing and regression safety: build the safety net as you go, for example characterization tests and replaying production-like data through old and new versions to compare outputs, because a wrong result here means someone is paid incorrectly.
• Releasing: get changes into production safely, with a rollback plan for each step.
• Collaboration: communicate clearly and proactively with engineers, product, and leadership, raise risks early, and be someone the team enjoys working with.

You’ll work alongside people who know the leave and absence domain well, so you won't be expected to learn it overnight. You will need to be curious enough to learn it as you go.

Required Experience

• Significant professional C#/.NET experience (roughly 8-10+ years), including real depth in .NET Framework 4.x.
• Has led or done much of the hands‑on work on a .NET Framework to modern .NET migration of a large system while it stayed in production. A greenfield rewrite or a small‑app port isn't the same thing.
• Solid MongoDB experience, including working through driver and server version upgrades.
• Comfortable in large, under‑tested legacy codebases. You know how to add regression safety before changing behavior.
• Uses AI coding tools every day (e.g., Claude Code, Cursor, Copilot) and backs their output with tests, review, and evidence.
• Strong communicator who can work independently inside a product team, gather requirements, and explain technical risk to non‑engineers.

Nice to Have

• Experience with .NET Standard 2.0 / multi‑targeting strategies for shared libraries during incremental migrations.
• HR tech, benefits, payroll, leave and absence, or other rules‑heavy business domains.
• Multi‑tenant SaaS and keeping each customer's data isolated.
• AWS, Docker, CI/CD (GitHub Actions, Jenkins), and structured logging or observability (e.g., Datadog).
• A second modern stack such as TypeScript/Node.js.

Why Devblock

• An established team: Devblock is a sizable software consultancy with engineers across the US, Canada, Costa Rica, and Vietnam.
• AI-forward in practice: we run an active AI engineering practice with regular knowledge‑sharing sessions and standardized agentic workflows, and our engineers ship real production work with tools like Claude Code every day. We pay for the AI tooling you need.
• Long‑term relationships: many of our client engagements run for years, some for over a decade.

We build teams to last.

• Room to grow with us: follow‑on work is a real possibility once this engagement wraps, especially for engineers who are excellent and adaptable.

Engagement Details

• Type: Contract, with an initial commitment of about 3 months and a potential to be extended.
• Start: As soon as possible.
• Hours: Full-time preferred.
• Location: Remote. Generally working US Pacific time is expected.

Company: Senior .NET Modernization Engineer (Remote - USA)

Rate: $100 – 120/hr

Location: New

United States only