Freelance Principal Software Engineer – Platform Architecture and Developer Enablement (Hands-O[...]

colayer; Deutschland; On-site; USD 120,000 - 150,000; Full time

Job summary

A software development firm is seeking a Principal Software Developer to lead the evolution of a critical platform. This role demands 8 to 12 years of hands-on software development experience with expertise in C#/.NET Core and functional programming. The candidate will be responsible for designing scalable software architectures and ensuring high-quality code delivery. Excellent communication skills and fluency in English are required, with German considered a strong plus. This is a full-time position in the United States, Ohio area.

Qualifications

• 8 to 12 years of professional software development experience.
• Fluent in modern engineering practices and clean code principles.
• Confident in working with relational databases and aware of CI/CD pipelines.

Responsibilities

• Design and build a business-critical software platform using modern frameworks.
• Spearhead migration from a semi-distributed to a scalable architecture.
• Champion tools and techniques that enhance engineering effectiveness.
• Operate close to production and support the software post-deployment.

Skills

C#/.NET Core

Functional programming

Strong static typing

Communication

Collaboration

Tools

Git

Docker

Kubernetes

Terraform

Job description

Overview

Project Duration: 6-12 months, extension possible

Commitment: Full-time

Job Description

Our client is looking for a hands-on Principal Software Developer with deep computer science fundamentals and a pragmatic, product-oriented mindset. You combine strong architectural thinking with the ability to ship high-quality code thoughtfully and predictably.

You are fluent in modern engineering practices, comfortable in heterogeneous, service-oriented and distributed environments, and focus on writing robust, maintainable code for systems that scale.

You will help evolve a business-critical platform—leading the transition from a heterogeneous semi-distributed codebase to a strategically aligned, reliable, and scalable architecture. You will balance delivery speed with long-term sustainability and champion tools and techniques that multiply engineering effectiveness.

What you\'ll do

• Design, build, and run a business-critical software platform using modern frameworks and programming languages
• Spearhead the migration from a semi-distributed codebase to a unified, scalable architecture
• Analyze trade-offs, risks, dependencies, and user value to drive technical decisions
• Solve complex technical problems hands-on, not from the sidelines
• Operate close to production: build it, ship it, support it
• Champion clean code, test coverage, and performance-first thinking
• Evaluate and apply emerging developer tools where they provide real leverage (e.g., GitHub Copilot, GPT agents, etc.)

Who we\'re looking for

• 8 to 12 years of professional experience in software development with at least 80–100% of your last 2-3 years spent coding, shipping, and deploying
• Expert knowledge of C#/.NET Core
• Proven track record of delivering production-grade systems
• Proficient in functional programming and strong static typing (F#, Scala 3, Rust, Haskell, Kotlin, OCaml, etc.)
• Applied architectural knowledge: modular monoliths, microservices, event-driven systems, actors, etc.
• Confident working with relational databases (schema design, migrations, tuning)
• Familiarity with modern delivery stacks: Git, GitOps, CI/CD, Docker, etc.
• Strong communication and collaboration skills; self-starter attitude
• Fluent English (C1/C2); German is a strong plus

Nice to Have

• Experience with Kubernetes and Infrastructure-as-Code tools (e.g. Terraform, Pulumi)
• Familiarity with AI-assisted engineering tools (Copilot, GPT, linters, analyzers)
• Experience with platform abstraction, developer enablement, or internal tooling