Senior .NET Modernization Engineer (Remote - LATAM)

Braintrust; United States; Remote; USD 69,000 - 76,000; Full time

Job summary

Braintrust is seeking an experienced engineer to modernize a decade-old .NET/MongoDB-based HR SaaS component. The role emphasizes deep coding, architectural judgment, and hands-on migration work while maintaining production stability.

You will collaborate with product teams, employ AI coding tools responsibly, and plan safe, incremental upgrades across the stack, including from .NET Framework to modern .NET and MongoDB driver upgrades. Remote with US time zones preferred.

Qualifications

• 8–10+ years of professional C#/.NET experience.
• Led or contributed to a .NET Framework to modern .NET migration while in production.
• Solid MongoDB experience and driver/server upgrades.
• Experience with AI coding tools and testing.

Responsibilities

• Analyze legacy .NET Framework systems and plan a safe migration path.
• Architect and sequence upgrade steps with minimal production risk.
• Write and review production code daily, using AI coding agents.
• Develop characterization tests and regression safety checks.
• Coordinate releasing with rollback plans and cross-team communication.
• Collaborate with product and leadership, surface risks early.

Skills

C#/.NET

Migration architecture

Communication

Tools

MongoDB

AI coding tools

Job description

• Rate: $50 – $55/hr
• Hours: 40 hours / week
• Experience: 10+ years
• Location: United States | Canada + 23 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 / nearshore 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.