---
name: dotnet-core-expert-25901e10aa73
description: Use when building .NET 8 applications with minimal APIs, clean architecture, or cloud-native microservices. Invoke for Entity Framework Core, CQRS with MediatR, JWT authentication, AOT compilation.
license: MIT
metadata:
  author: https://github.com/Jeffallan
  version: "1.1.0"
  domain: backend
  triggers: .NET Core, .NET 8, ASP.NET Core, C# 12, minimal API, Entity Framework Core, microservices .NET, CQRS, MediatR
  role: specialist
  scope: implementation
  output-format: code
  related-skills: fullstack-guardian, microservices-architect, cloud-architect, test-master
---

# .NET Core Expert

## Core Workflow

1. **Analyze requirements** — Identify architecture pattern, data models, API design
2. **Design solution** — Create clean architecture layers with proper separation
3. **Implement** — Write high-performance code with modern C# features; run `dotnet build` to verify compilation — if build fails, review errors, fix issues, and rebuild before proceeding
4. **Secure** — Add authentication, authorization, and security best practices
5. **Test** — Write comprehensive tests with xUnit and integration testing; run `dotnet test` to confirm all tests pass — if tests fail, diagnose failures, fix the implementation, and re-run before continuing; verify endpoints with `curl` or a REST client

## Reference Guide

Load detailed guidance based on context:

| Topic | Reference | Load When |
|-------|-----------|-----------|
| Minimal APIs | `references/minimal-apis.md` | Creating endpoints, routing, middleware |
| Clean Architecture | `references/clean-architecture.md` | CQRS, MediatR, layers, DI patterns |
| Entity Framework | `references/entity-framework.md` | DbContext, migrations, relationships |
| Authentication | `references/authentication.md` | JWT, Identity, authorization policies |
| Cloud-Native | `references/cloud-native.md` | Docker, health checks, configuration |

## Constraints

### MUST DO
- Use .NET 8 and C# 12 features
- Enable nullable reference types: `<Nullable>enable</Nullable>` in the `.csproj`
- Use async/await for all I/O operations — e.g., `await dbContext.Users.ToListAsync()`
- Implement proper dependency injection
- Use record types for DTOs — e.g., `public record UserDto(int Id, string Name);`
- Follow clean architecture principles
- Write integration tests with `WebApplicationFactory<Program>`
- Configure OpenAPI/Swagger documentation

### MUST NOT DO
- Use synchronous I/O operations
- Expose entities directly in API responses
- Skip input validation
- Use legacy .NET Framework patterns
- Mix concerns across architectural layers
- Use deprecated EF Core patterns

## Code Examples

### Minimal API Endpoint
```csharp
// Program.cs
var builder = WebApplication.CreateBuilder(args);
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();
builder.Services.AddMediatR(cfg => cfg.RegisterServicesFromAssembly(typeof(Program).Assembly));

var app = builder.Build();
app.UseSwagger();
app.UseSwaggerUI();

app.MapGet("/users/{id}", async (int id, ISender sender, CancellationToken ct) =>
{
    var result = await sender.Send(new GetUserQuery(id), ct);
    return result is null ? Results.NotFound() : Results.Ok(result);
})
.WithName("GetUser")
.Produces<UserDto>()
.ProducesProblem(404);

app.Run();
```

### MediatR Query Handler
```csharp
// Application/Users/GetUserQuery.cs
public record GetUserQuery(int Id) : IRequest<UserDto?>;

public sealed class GetUserQueryHandler : IRequestHandler<GetUserQuery, UserDto?>
{
    private readonly AppDbContext _db;

    public GetUserQueryHandler(AppDbContext db) => _db = db;

    public async Task<UserDto?> Handle(GetUserQuery request, CancellationToken ct) =>
        await _db.Users
            .AsNoTracking()
            .Where(u => u.Id == request.Id)
            .Select(u => new UserDto(u.Id, u.Name))
            .FirstOrDefaultAsync(ct);
}
```

### EF Core DbContext with Async Query
```csharp
// Infrastructure/AppDbContext.cs
public sealed class AppDbContext(DbContextOptions<AppDbContext> options) : DbContext(options)
{
    public DbSet<User> Users => Set<User>();

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.ApplyConfigurationsFromAssembly(typeof(AppDbContext).Assembly);
    }
}

// Usage in a service
public async Task<IReadOnlyList<UserDto>> GetAllAsync(CancellationToken ct) =>
    await _db.Users
        .AsNoTracking()
        .Select(u => new UserDto(u.Id, u.Name))
        .ToListAsync(ct);
```

### DTO with Record Type
```csharp
public record UserDto(int Id, string Name);
public record CreateUserRequest(string Name, string Email);
```

## Output Templates

When implementing .NET features, provide:
1. Project structure (solution/project files)
2. Domain models and DTOs
3. API endpoints or service implementations
4. Database context and migrations if applicable
5. Brief explanation of architectural decisions

[Documentation](https://jeffallan.github.io/claude-skills/skills/backend/dotnet-core-expert/)


---
Source attribution: andrewthomastaylor
Original project: https://github.com/andrewthomastaylor/Skills/blob/cb7b4065bacb4b06224de86d509ccef568f68b79/claude-skills/skills/dotnet-core-expert/SKILL.md
License: MIT
License information: https://opensource.org/license/mit
Original upstream instructions; downloaded from Mega AI Hub.

## Upstream license notice

MIT License

Copyright (c) 2025

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.



# Mega AI Hub resource metadata

Creator / publisher: andrewthomastaylor
Original project: https://github.com/andrewthomastaylor/Skills/blob/cb7b4065bacb4b06224de86d509ccef568f68b79/claude-skills/skills/dotnet-core-expert/SKILL.md
Attribution basis: Source repository record

Fields of work: Development & Engineering, Product Management
Roles: Backend Developer, Full-Stack Developer, Product Manager, Technical Product Manager
Specialties: Backend
Tools: Tool not specified
Country applicability: Country not specified
Classification basis: Source catalog labels
Instruction SHA-256: 968ea2e3df1850f93c06ae3b66045cd128d8b276fab6e15f7bbd560fad38f1db