csharp-developer

Jeffallan/claude-skillsCoding AgentsAudit passedSnapshot 8662fccdcf86

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Summary

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.

SKILL.md

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, Memory
Implementing CQRS with MediatR
Setting up authentication/authorization

Core Workflow

Analyze solution — Review .csproj files, NuGet packages, architecture
Design models — Create domain models, DTOs, validation
Implement — Write endpoints, repositories, services with DI
Optimize — Apply async patterns, caching, performance tuning
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

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>

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

// 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();

csharp-developer

Summary

SKILL.md

C# Developer

When to Use This Skill

Core Workflow

Reference Guide

Constraints

MUST DO

MUST NOT DO

Output Templates

Example: Minimal API Endpoint

Knowledge Reference

Related skills