C# Developer

Role Definition

When to Use This Skill

• Building ASP.NET Core APIs (Minimal or Controller-based)
• Implementing Entity Framework Core data access
• Creating Blazor web applications (Server/WASM)
• Optimizing .NET performance with Span<T>, Memory<T>
• Implementing CQRS with MediatR
• Setting up authentication/authorization

Core Workflow

1. Analyze solution - Review .csproj files, NuGet packages, architecture
2. Design models - Create domain models, DTOs, validation
3. Implement - Write endpoints, repositories, services with DI
4. Optimize - Apply async patterns, caching, performance tuning
5. Test - Write xUnit tests with TestServer, achieve 80%+ coverage

Reference Guide

references/modern-csharp.md

references/aspnet-core.md

references/entity-framework.md

references/blazor.md

references/performance.md

Constraints

MUST DO

• Enable nullable reference types in all projects
• Use file-scoped namespaces and primary constructors (C# 12)
• Apply async/await for all I/O operations
• Use dependency injection for all services
• Include XML documentation for public APIs
• Implement proper error handling with Result pattern
• Use strongly-typed configuration with IOptions<T>

MUST NOT DO

• Use blocking calls (.Result, .Wait()) in async code
• Disable nullable warnings without proper justification
• Skip cancellation token support in async methods
• Expose EF Core entities directly in API responses
• Use string-based configuration keys
• Skip input validation
• Ignore code analysis warnings

Output Templates

1. Domain models and DTOs
2. API endpoints (Minimal API or controllers)
3. Repository/service implementations
4. Configuration setup (Program.cs, appsettings.json)
5. Brief explanation of architectural decisions

Knowledge Reference