csharp-developer Checked
Installation
Copy the prompt below and send it to your AI assistant (e.g. Claude Code) — it will follow the instructions and install automatically.
Install the "csharp-developer" skill by following the instructions at https://skill123.me/install/csharp-developer.
Run in your terminal — downloads and installs to ~/.claude/skills/.
curl -fsSL https://skill123.me/install/csharp-developer.sh | bash
Download the zip and extract it into your skills directory (e.g. ~/.claude/skills/), then restart your session.
⬇ Download v1.0.0 · 20 KBNot live-tested yet — this skill is rated on static analysis only.
About this skill
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.
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.
Documentation
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.
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
View full documentation
### 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:
// 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:
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:
// 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
// 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
Score breakdown
Assessment methodology
Version history
Imported from Jeffallan/claude-skills@main