Full-timeOn-siteHot Position

Senior Fullstack Developer (.Net) - Onsite Finland

Engineering

Helsinki, Finland

Salary

Negotiable

Posted

Posted yesterday

About This Role

We're looking for a backend engineer to join a team that's doing something many talk about but few actually execute well: taking a large, living industrial software platform from its legacy roots to a modern .NET stack, without breaking what's already working in production. This isn't a greenfield build. You'll be working inside a mature, complex codebase, making careful architectural decisions about what to migrate, how to migrate it, and how to keep everything running smoothly along the way. If you enjoy untangling systems, improving performance, and writing clean C# — this is your kind of project.

What You Will Do

Your key responsibilities in this role

What You Will Do

•Work on a phased migration from legacy .NET Framework toward standard modern .NET components.
•Write and refactor backend services, keeping production systems stable throughout.
•Optimize database interactions and troubleshoot performance bottlenecks.
•Shape API contracts in close collaboration with frontend developers.
•Continuously improve the health and maintainability of a production system that real users depend on.

What We Are Looking For

Required skills and qualifications

Technical Skills

5+ years of backend engineering experience with C# and .NET.
Strong ASP.NET Core and LINQ skills with solid async/parallel programming knowledge.
Real-world EF Core experience — migrations, transactions, and performance awareness.
SQL Server proficiency: query tuning, execution plans, and diagnosing slow queries.
Comfort navigating and debugging large, unfamiliar codebases.
Familiarity with CI/CD workflows (Azure DevOps or similar).
Sound algorithmic thinking — time/space complexity and choosing the right approach.

Benefits & Perks

What we offer to our team members

1. Lunch benefit

•Top-up requests are made in the Edenred web or mobile app
•The company will approve the requests on the 25th of every month and the money is available on your cards on the 1st day of the month
•Max 21 coupons per month (1 per working day)
•The company pays the tax-free value of the benefit, 25%
•The rest, 75%, is deducted from the net salary

2. Recreational Benefits

•400 EUR per year, paid in four equal installments
•You can transfer the money to the massage and/or transport benefit from the Edenred app
•Can be used for sports, theater, cinema, yoga, concert tickets, etc.

3. Excessive health care insurance

•Covers general doctor appointments without a deductible and the company pays the deductible for specialist appointments. Thus, it’s completely free to use for you.
•It also covers all necessary procedures and tests as prescribed by the doctor
•The easiest way is to contact Mehiläinen and inform them that you are covered by Tekai insurance
•If you use other medical providers, you need to pay yourself first and submit the receipts to Trung or Lähitapiola directly to get reimbursement

4. Annual Health check

•Practicalities to be updated soon

5. Personal budget

•We have a Personal Budget for the employee

6. Annual company trip

•The company provides an annual off-site for the whole team
•The destination is decided by voting

7. Phone benefit

•The company pays for phone subscriptions. The number is released to you in case you resign
•Taxable value, 20€, is added to your salary

8. Lunch / Hangout

•The company arranges lunches, dinners, and activities based on the team's wishes
•Goal is to have at least one lunch and one after-work event (dinner, activity) each month
•Use #eat-see-play channel for proposing restaurants and/or activities

9. Birthday wishlist

•Submit your wish to us
•Value max 100 eur incl. VAT
•The team will order the item for you

10. How We Work:

•This is a hybrid role based in Helsinki. You'll come into the office 2–3 days per week — enough to stay connected with the team — and work the rest of the time remotely. Core hours are 9:00 AM to 6:00 PM, Monday to Friday, with a 1.5-hour lunch break built into the day. We find this rhythm gives people the focus time they need while keeping collaboration strong.