MCPInstall

csharp-developer

by jeffallanBackend & APIs

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.

Installs
4.8K
Last 24h
+28
Trending rank
#4603
Security
Fail

Install

Works with every agent the skills CLI supports.

npx skills add https://github.com/jeffallan/claude-skills --skill csharp-developer
  1. 01

    Install

    Run the command in your project. The CLI asks which agents to install for.

  2. 02

    Describe the task

    Ask your agent for something this skill covers. It loads csharp-developer automatically when relevant.

  3. 03

    Review the result

    The agent follows the SKILL.md steps, scripts and references bundled with the skill.

Security audits

Independent scans of the skill's instructions and bundled files.

Gen Agent Trust Hub FailCRITICAL ·Automated security scanners have flagged the documentation link in this skill as a malicious blacklisted URL. While the core functionality and code samples appear standard for C# development, the external reference to the author's GitHub Pages site poses a risk. Additionally, the skill's reliance on processing user-provided project files without clear isolation creates a surface for indirect prompt injection.
Socket PassNo alerts
Snyk PassLOW ·Risk: LOW · No issues
Runlayer PassLOW ·1/6 files flagged
ZeroLeaks PassNONE ·Score: 93/100 · 2 sections analyzed

SKILL.md

The instructions your agent reads when the skill is triggered.

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:

TopicReferenceLoad When
Modern C#references/modern-csharp.mdRecords, pattern matching, nullable types
ASP.NET Corereferences/aspnet-core.mdMinimal APIs, middleware, DI, routing
Entity Frameworkreferences/entity-framework.mdEF Core, migrations, query optimization
Blazorreferences/blazor.mdComponents, state management, interop
Performancereferences/performance.mdSpan<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: 
    // 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

Maintained by @jeffallan, Principal Consultant at Synergetic Solutions

Documentation

FAQ

What does the csharp-developer skill do?

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.

How do I install csharp-developer?

Run npx skills add https://github.com/jeffallan/claude-skills --skill csharp-developer in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/csharp-developer/ (personal) or .claude/skills/csharp-developer/ (project).

Which AI agents can use csharp-developer?

Any agent that supports the open Agent Skills format (a folder with a SKILL.md file), including Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, Windsurf, Cline, OpenCode and more.

Is csharp-developer safe to install?

Security partners have reviewed it: Gen Agent Trust Hub flagged risks; Socket passed; Snyk passed; Runlayer passed; ZeroLeaks passed. As with any skill, read the SKILL.md and bundled scripts before installing.

Who maintains csharp-developer?

It is published by jeffallan in jeffallan/claude-skills. It has 4,830 recorded installs.

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