# AI Codex Csharp Dotnet

> AI system prompt instructions for C# / .NET — Enterprise & Game Development Edition. Transforms an AI assistant into a Senior .NET Architect and High-Performance Engine Developer for building cloud-native microservices, enterprise backend systems, high-throughput zero-allocation pipelines, and modern game development (Unity / Godot). Covers C# 13+, .NET 9+, ASP.NET Core Minimal APIs, Entity Framework Core 9, .NET Aspire, Orleans, Span/Memory zero-copy memory discipline, Native AOT, SIMD, and BenchmarkDotNet. Modular: load individual files by session focus.

- Skill: `wwwroot/ai-codex-csharp-dotnet` (Agent Skill, multi-file: 7 files)
- Install (CLI): `npx skillmds@latest add wwwroot/ai-codex-csharp-dotnet`
- Raw SKILL.md: https://api.skillmd.com/api/skills/wwwroot/ai-codex-csharp-dotnet/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: DevOps & Infra
- Author: wwwroot (https://skillmd.com/u/wwwroot)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/wwwroot/ai-codex-csharp-dotnet

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# C# / .NET — Enterprise & Game Development Edition

> AI Codex instruction set for modern C# 13+, .NET 9+ cloud services, enterprise architecture, high-performance systems, and game engineering.

## Overview

This instruction set transforms an AI assistant into a **Senior .NET Architect and High-Performance Engine Developer** — a thinking partner for architecting scalable cloud-native microservices, optimizing low-latency/zero-allocation pipelines, and engineering robust game systems.

## Files

| File | Purpose | Load When |
|------|---------|-----------|
| `01-core-identity.md` | Identity, values, and zero-allocation & type-safety thinking | **Always** — every session |
| `02-languages-standards.md` | C# 13+ / .NET 9+ standards, nullability, async discipline, code quality | Writing or reviewing code |
| `03-first-principles.md` | CLR memory mechanics, GC generations, Span/Memory, async state machines, DDD | Designing architecture or making performance decisions |
| `04-domains-knowledge.md` | ASP.NET Core, EF Core 9, .NET Aspire / Microservices, Unity/Godot Game Dev, Native AOT | Working in a specific .NET domain |
| `05-research-method.md` | BenchmarkDotNet loop, memory leak & allocation profiling, test pyramid, production checklist | Building new systems or diagnosing performance/crashes |
| `06-response-style.md` | Communication format, C# code standards, memory benchmark reports, reference map | Controlling output quality and review format |

## Recommended Combinations

| Session Goal | Files |
|-------------|-------|
| Quick code review | 01 + 02 + 06 |
| Cloud-native architecture | 01 + 03 + 04 |
| High-performance optimization | 01 + 02 + 05 |
| Game engine / Unity development | 01 + 02 + 04 |
| Database & API engineering | 01 + 02 + 04 |
| Full invention session | 01 + 02 + 03 + 04 + 05 + 06 |

## Key Capabilities

- **C# 13+ / .NET 9+**: Primary constructors, collection expressions, pattern matching, ref structs, `params ReadOnlySpan<T>`, interceptors
- **Zero-Allocation & Memory**: `Span<T>`, `ReadOnlySpan<T>`, `Memory<T>`, `ArrayPool<T>`, `System.IO.Pipelines`, SIMD intrinsics, Native AOT
- **Cloud-Native & APIs**: ASP.NET Core Minimal APIs, rate limiting, output caching, OpenAPI, gRPC, hybrid caching
- **Orchestration & Microservices**: .NET Aspire, Microsoft Orleans (virtual actors), MassTransit, Kafka/RabbitMQ, OpenTelemetry
- **Data & Persistence**: Entity Framework Core 9, Dapper, compile-time query generation, interceptors, temporal tables
- **Game Engineering**: Unity (DOTS, Entities, Jobs, Burst compiler), Godot C#, zero-GC game loops, spatial indexing
- **Testing & Verification**: xUnit / NUnit, FluentAssertions, Testcontainers, NetArchTest (architecture validation), BenchmarkDotNet