Fullstack Engineer (.NET / React) – AI-Native Spec-Driven Delivery

Seargin Ltd

Warszawa

Hybrid

PLN 180,000 - 270,000

Full time

3 days ago
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Benefits offered by this job

B2B Contract
MultiSport
Private Medical Care
International Projects

Job summary

Seargin Ltd in Warsaw is seeking aSenior Full-Stack Engineer to design and implement scalable architectures across .NET and React stacks. You will translate clear specifications into working code using AI-assisted tools and validate code through rigorous testing and security checks.

You will collaborate with PMs and BAs, participate in client workshops, and ensure fast, predictable delivery within a dynamic, international firm. Strong Polish and English communication are essential.

Qualifications

  • 5+ years of commercial full-stack engineering experience with independent responsibility for project architecture.
  • Very good knowledge of .NET and C#, including Web API and Entity Framework Core.
  • React with TypeScript for modern frontend development.
  • Proven AI-assisted code generation and refactoring workflow with explainable validation.
  • Experience with spec-driven or test-driven development and solid test coverage.
  • Good knowledge of REST APIs, SQL Server or PostgreSQL, Git, and CI/CD.
  • Ability to work independently and own delivery in a small team.

Responsibilities

  • Design and maintain scalable architecture across .NET backend and React frontend.
  • Translate specs into working code using AI-assisted tools.
  • Review and validate code with testing, security, and readability checks.
  • Collaborate with PMs, BAs, and client workshops; participate in demos.
  • Coordinate with DevOps on CI/CD and environments; partner with QA on testing.

Skills

Full-Stack
.NET & C#
React TS
AI-assisted Development
Spec-Driven TD
REST APIs
Relational DBs
Delivery Ownership
Polish & English

Tools

Git
CI/CD
Azure

Job description

  • Design simple, predictable, and maintainable application architecture across .NET backend and React frontend
  • Specification-Driven Development
    • Translate clear specifications and requirements into working code using AI-assisted development tools
  • Code Quality & Validation
    • Review and validate both personal and AI-generated code through testing, edge-case analysis, security checks, and readability reviews
  • Testing & Coverage
    • Apply rigorous testing practices and ensure implementation provides reliable coverage against defined requirements
  • Business Collaboration
    • Work closely with PMs and BAs to clarify specifications and participate in client workshops and demonstrations
  • Collaborate with DevOps on CI/CD and environments and with QA on testing activities and acceptance criteria
  • Spec-Driven Delivery
    • Work in short iterations with clear specifications, fast implementation, regular client demos, and predictable progress
  • Documentation & Handover
    • Maintain clear documentation and repeatable solutions to support smooth project handover and future development
Requirements
  • Full-Stack Experience
    • 5+ years of commercial full-stack engineering experience with independent responsibility for project architecture
  • Very good knowledge of .NET and C#, including Web API and Entity Framework Core
  • React & TypeScript
    • Very good knowledge of React with TypeScript for modern frontend development
  • AI-Assisted Development
    • Proven personal workflow for AI-assisted code generation and refactoring with the ability to explain how AI-generated output is validated
  • Spec-Driven & Test-Driven Development
    • Hands-on experience with spec-driven or test-driven development and the ability to work from specifications with solid test coverage
  • Development Best Practices
    • Good knowledge of REST APIs, relational databases such as SQL Server or PostgreSQL, Git, and CI/CD
  • Delivery Ownership
    • Ability to work independently and take full ownership of delivery within a small team and tight timelines
  • Business Communication
    • Strong Polish and English communication skills with confidence participating in discussions with enterprise clients
What we offer
  • B2B Contract
    • Employment based on a B2B contract
  • Stable and Dynamic International Firm
    • Opportunity to work in a stable, dynamically developing international company
  • Engaging Projects and Latest IT
    • Chance to participate in interesting projects and work with the latest information technologies
  • Competitive Rates
    • Attractive remuneration rates offeres
  • Renowned International Projects
    • Involvement in the most prestigious international project
  • MultiSport and Private Medical Care
    • MultiSport and Private Medical Care
Nice to have
  • Experience working directly with enterprise clients or in a Forward Deployed Engineer-type role
  • Understanding of data modelling for reporting and collaboration with Power BI teams
  • Experience with Azure, including App Service and Azure SQL, or another cloud platform
  • Experience working in a consulting or project-based environment

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