dotnet-csharp

name	dotnet-csharp
description	Baseline C# skill loaded for every .NET code path. Guides language patterns (records, pattern matching, primary constructors, C# 8-15), coding standards, async/await, DI, LINQ, serialization, domain modeling, concurrency, Roslyn analyzers, globalization, native interop (P/Invoke, LibraryImport, ComWrappers), WASM interop (JSImport/JSExport), and type design. Spans 27 topics. Do not use for ASP.NET endpoint architecture, UI framework patterns, or CI/CD guidance.
license	MIT
user-invocable	false

dotnet-csharp

Overview

C# language patterns, coding standards, and .NET runtime features for idiomatic, performant code. This consolidated skill spans 25 topic areas. Load the appropriate companion file from references/ based on the routing table below.

Always-Load Baseline

These references define correctness and quality standards that apply to all C# code — load them by default whenever producing or reviewing code, regardless of what the user asked for:

Path resolution note: The filenames below are relative to the subdirectory of this skill. The Read tool needs an absolute path. Use Glob to locate each file (pattern: ), then pass the absolute path to Read. and are in the parent directory — Glob for and .

• — naming conventions, file layout, style rules
• — async/await correctness, ConfigureAwait, cancellation propagation (nearly all .NET code uses async)
• — SOLID, DRY, single responsibility, dependency inversion, anti-pattern detection
• — common mistakes the agent should avoid without being told (async void, DI lifetime misuse, swallowed exceptions)
• — side-by-side BAD/GOOD code: DateTime.Now→TimeProvider, N+1 queries, DI lifetime mismatch, .Result deadlocks, CancellationToken propagation
• — always prefer free/open-source: MediatR→Mediator(MIT), FluentValidation→AddValidation(), AutoMapper→Mapperly, Newtonsoft→STJ, Swashbuckle→Microsoft.AspNetCore.OpenApi
• — when to use what: consolidated decision guides for architecture, data access, caching, DI, observability, testing, deployment (Glob: )
• — one-page summary of all non-negotiable rules, patterns, and package alternatives (Glob: )
• — .NET 10/11 and C# 14/15 features, version matrix, TFM-specific code generation rules

On-Demand References

Load these when the topic matches (see Routing Table keywords):

Routing Table

Topic	Keywords	Description	Companion File
Coding standards	naming, file layout, style rules	Baseline C# conventions (naming, layout, style rules)	references/coding-standards.md
Async/await	async, Task, ConfigureAwait, cancellation	async/await, Task patterns, ConfigureAwait, cancellation	references/async-patterns.md
Dependency injection	DI, services, scopes, keyed, lifetimes	MS DI, keyed services, scopes, decoration, lifetimes	references/dependency-injection.md
Configuration	Options pattern, user secrets, feature flags	Options pattern, user secrets, feature flags, IOptions<T>	references/configuration.md
Source generators	IIncrementalGenerator, GeneratedRegex, LoggerMessage	IIncrementalGenerator, GeneratedRegex, LoggerMessage, STJ	references/source-generators.md
Nullable reference types	annotations, migration, agent mistakes	Annotation strategies, migration, agent mistakes	references/nullable-reference-types.md
Serialization	System.Text.Json, Protobuf, MessagePack, AOT	System.Text.Json source generators, Protobuf, MessagePack	references/serialization.md
Channels	Channel<T>, bounded/unbounded, backpressure	Channel<T>, bounded/unbounded, backpressure, drain	references/channels.md
LINQ optimization	IQueryable vs IEnumerable, compiled queries	IQueryable vs IEnumerable, compiled queries, allocations	references/linq-optimization.md
Domain modeling	aggregates, value objects, domain events	Aggregates, value objects, domain events, repositories	references/domain-modeling.md
SOLID principles	SRP, DRY, anti-patterns, compliance checks	SOLID and DRY principles, C# anti-patterns, fixes	references/solid-principles.md
Concurrency	lock, SemaphoreSlim, Interlocked, concurrent collections	lock, SemaphoreSlim, Interlocked, concurrent collections	references/concurrency-patterns.md
Roslyn analyzers	DiagnosticAnalyzer, CodeFixProvider, multi-version	DiagnosticAnalyzer, CodeFixProvider, CodeRefactoring	references/roslyn-analyzers.md
Editorconfig	IDE/CA severity, AnalysisLevel, globalconfig	IDE/CA severity, AnalysisLevel, globalconfig, enforcement	references/editorconfig.md
File I/O	FileStream, RandomAccess, FileSystemWatcher, paths	FileStream, RandomAccess, FileSystemWatcher, MemoryMappedFile	references/file-io.md
Native interop	P/Invoke, LibraryImport, ComWrappers, marshalling	P/Invoke, LibraryImport, ComWrappers, marshalling, cross-platform	references/native-interop.md
Input validation	.NET 10 AddValidation, DataAnnotations	.NET 10 AddValidation, DataAnnotations, ProblemDetails	references/input-validation.md
Validation patterns	DataAnnotations, IValidatableObject, IValidateOptions	DataAnnotations, IValidatableObject, IValidateOptions<T>	references/validation-patterns.md
Modern patterns	records, pattern matching, primary constructors	Records, pattern matching, primary constructors, C# 12-15	references/modern-patterns.md
API design	naming, parameter ordering, return types, extensions	Naming, parameter ordering, return types, error patterns	references/api-design.md
Type design/perf	struct vs class, sealed, Span/Memory, collections	struct vs class, sealed, Span/Memory, collections	references/type-design-performance.md
Code smells	anti-patterns, async misuse, DI mistakes, fixes	Anti-patterns, async misuse, DI mistakes, fixes	references/code-smells.md
.NET releases	.NET 10, .NET 11, C# 14, C# 15, TFM, version, union, extension blocks, field keyword	Version matrix, new features, TFM-specific code generation	references/dotnet-releases.md
Globalization	CultureInfo, StringComparison, TimeZoneInfo, Rune, encoding	Culture-aware coding, string comparison, time zones, character processing	references/globalization.md
WASM interop	JSImport, JSExport, standalone WASM, wasm-experimental, browser	JSImport/JSExport, standalone .NET WASM, browser APIs, WASM AOT	references/wasm-interop.md

Scope

• C# language features (C# 8-15)
• .NET runtime patterns (async, DI, config, serialization, channels, LINQ)
• Code quality (analyzers, editorconfig, code smells, SOLID)
• Type design and domain modeling
• File I/O and native interop
• Globalization (string comparison, CultureInfo, time zones, character processing, encoding)
• Input validation at the model level (DataAnnotations, IValidatableObject, Options validation)

Out of scope

• ASP.NET Core / web API patterns (request-level validation, endpoint filters) -> [skill:dotnet-api]
• UI framework patterns -> [skill:dotnet-ui]
• Testing patterns -> [skill:dotnet-testing]
• Build/MSBuild/project setup -> [skill:dotnet-tooling]
• Performance profiling tools -> [skill:dotnet-tooling]