---
name: csharp-developer-cb0c509d3bc6
description: "Use when building C# applications with .NET 8+, ASP.NET Core APIs, or Blazor web apps. Builds REST APIs using minimal or controller-based routing, configures database access with Entity Framework Core, implements async patterns and cancellation, structures applications with CQRS via MediatR, and scaffolds Blazor components with state management. Invoke for C#, .NET, ASP.NET Core, Blazor, Entity Framework, EF Core, Minimal API, MAUI, SignalR."
license: MIT
metadata:
  author: https://github.com/Jeffallan
  version: "1.1.0"
  domain: language
  triggers: C#, .NET, ASP.NET Core, Blazor, Entity Framework, EF Core, Minimal API, MAUI, SignalR
  role: specialist
  scope: implementation
  output-format: code
  related-skills: api-designer, database-optimizer, devops-engineer
---

# C# Developer

Senior C# developer with mastery of .NET 8+ and Microsoft ecosystem. Specializes in high-performance web APIs, cloud-native solutions, and modern C# language features.

## 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; verify 80%+ coverage

> **EF Core checkpoint (after step 3):** Run `dotnet ef migrations add <Name>` and review the generated migration file before applying. Confirm no unintended table/column drops. Roll back with `dotnet ef migrations remove` if needed.

## Reference Guide

Load detailed guidance based on context:

| Topic | Reference | Load When |
|-------|-----------|-----------|
| Modern C# | `references/modern-csharp.md` | Records, pattern matching, nullable types |
| ASP.NET Core | `references/aspnet-core.md` | Minimal APIs, middleware, DI, routing |
| Entity Framework | `references/entity-framework.md` | EF Core, migrations, query optimization |
| Blazor | `references/blazor.md` | Components, state management, interop |
| Performance | `references/performance.md` | Span<T>, async, memory optimization, AOT |

## 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 — always accept and forward `CancellationToken`:
  ```csharp
  // Correct
  app.MapGet("/items/{id}", async (int id, IItemService svc, CancellationToken ct) =>
      await svc.GetByIdAsync(id, ct) is { } item ? Results.Ok(item) : Results.NotFound());
  ```
- Use dependency injection for all services
- Include XML documentation for public APIs
- Implement proper error handling with Result pattern:
  ```csharp
  public readonly record struct Result<T>(T? Value, string? Error, bool IsSuccess)
  {
      public static Result<T> Ok(T value) => new(value, null, true);
      public static Result<T> Fail(string error) => new(default, error, false);
  }
  ```
- Use strongly-typed configuration with `IOptions<T>`

### MUST NOT DO
- Use blocking calls (`.Result`, `.Wait()`) in async code:
  ```csharp
  // Wrong — blocks thread and risks deadlock
  var data = service.GetDataAsync().Result;

  // Correct
  var data = await service.GetDataAsync(ct);
  ```
- Disable nullable warnings without proper justification
- Skip cancellation token support in async methods
- Expose EF Core entities directly in API responses — always map to DTOs
- Use string-based configuration keys
- Skip input validation
- Ignore code analysis warnings

## Output Templates

When implementing .NET features, provide:
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

## Example: Minimal API Endpoint

```csharp
// Program.cs (file-scoped, .NET 8 minimal API)
var builder = WebApplication.CreateBuilder(args);
builder.Services.AddScoped<IProductService, ProductService>();

var app = builder.Build();

app.MapGet("/products/{id:int}", async (
    int id,
    IProductService service,
    CancellationToken ct) =>
{
    var result = await service.GetByIdAsync(id, ct);
    return result.IsSuccess ? Results.Ok(result.Value) : Results.NotFound(result.Error);
})
.WithName("GetProduct")
.Produces<ProductDto>()
.ProducesProblem(404);

app.Run();
```

## Knowledge Reference

C# 12, .NET 8, ASP.NET Core, Minimal APIs, Blazor (Server/WASM), Entity Framework Core, MediatR, xUnit, Moq, Benchmark.NET, SignalR, gRPC, Azure SDK, Polly, FluentValidation, Serilog


---
Source attribution: https://github.com/Jeffallan
Original project: https://github.com/julio211916/TlantiCAD-Studio-V0.1-alpha/blob/590aa4fe05d1ec71a02ee9cc76c9a20508b5bcea/skills/ju/skills/csharp-developer/SKILL.md
License: MIT
License information: https://opensource.org/license/mit
Original upstream instructions; downloaded from Mega AI Hub.

## Upstream license notice

MIT License

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: https://github.com/Jeffallan
Original project: https://github.com/julio211916/TlantiCAD-Studio-V0.1-alpha/blob/590aa4fe05d1ec71a02ee9cc76c9a20508b5bcea/skills/ju/skills/csharp-developer/SKILL.md
Attribution basis: Source repository record

Fields of work: Development & Engineering, Product Management
Roles: Backend Developer, Full-Stack Developer, DevOps / SRE, Product Manager, Technical Product Manager
Specialties: Backend, API
Tools: .Net, Entity Framework, Asp.Net Core, Blazor
Country applicability: Country not specified
Classification basis: Source category, role and specialization labels
Instruction SHA-256: 521bde10becf940001c7b6724c7cc3c60687450f8082aaaaf196e06a906270d3