csharp-developer

csharp-developer is a skill for Claude Code, Codex from zacklecon/claude-skills. It costs 47 tokens per session (800 once invoked), scanned A, original, MIT.

Guidance for building C# applications with modern .NET, including ASP.NET Core APIs, Blazor web apps, and Entity Framework Core for database access. It also covers authentication, asynchronous code, and common application structure.

In plain words
What is it for?
Use it to build web APIs, Blazor applications, database models and queries, authentication and authorization, asynchronous services, CQRS features, and xUnit tests.
Why use it?
It helps choose appropriate .NET patterns while keeping APIs, database access, and authorization organized. It also addresses performance and automated testing concerns.

Skill for Claude CodeCodex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/zacklecon/claude-skills/csharp-developer
Any agent
npx skills add zacklecon/claude-skills --skill csharp-developer
Clone the repo
git clone --depth 1 https://github.com/zacklecon/claude-skills

Made for: Claude Code, Codex.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for csharp-developer

README.md
[![agentmods](https://agentmods.dev/badge/skills/zacklecon/claude-skills/csharp-developer.svg)](https://agentmods.dev/skills/zacklecon/claude-skills/csharp-developer)
Your own site
<a href="https://agentmods.dev/skills/zacklecon/claude-skills/csharp-developer"><img src="https://agentmods.dev/badge/skills/zacklecon/claude-skills/csharp-developer.svg" alt="Measured on agentmods" height="20"></a>
Per session 47 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 800 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00047 $0.00800
Opus 5 $0.00023 $0.00400
Sonnet 5 $0.00009 $0.00160
Haiku 4.5 $0.00005 $0.00080

Measured 4d ago against content hash ce9c58fc4ce1, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

csharp-developer scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 4d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

skills/csharp-developer/SKILL.md · 85 lines

How it starts

The opening of the file, as written. The whole thing — 85 lines — stays where its author put it; the contents beside it link to each section on GitHub.

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.

Role Definition

You are a senior C# developer with 10+ years of .NET experience. You specialize in ASP.NET Core, Blazor, Entity Framework Core, and modern C# 12 features. You build scalable, type-safe applications with clean architecture patterns and focus on performance optimization.

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

  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, achieve 80%+ coverage

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, 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
  • Use dependency injection for all services
  • Include XML documentation for public APIs
  • Implement proper error handling with Result pattern
  • Use strongly-typed configuration with IOptions

Read the full file on GitHub · 85 lines

Files

What ships with it

5 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 4d ago First seen · 85 lines · 47 tokens per session scan A ce9c58fc4ce1

Subscribe to this mod's changes

csharp-developer is a skill published in the GitHub repository zacklecon/claude-skills (3 stars, last pushed today), licensed MIT. It adds 47 tokens to every session and 800 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.

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