# Dotnet Guidelines

> dotnet coding guidelines and best practices. MUST follow these rules. Use when reviewing or writing .NET code or tasks.

- Skill: `majiayu000/dotnet-guidelines` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add majiayu000/dotnet-guidelines`
- Raw SKILL.md: https://api.skillmd.com/api/skills/majiayu000/dotnet-guidelines/raw
- Safety review: pending (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: majiayu000 (https://skillmd.com/u/majiayu000)
- Updated: 2026-09-09
- Page: https://skillmd.com/skills/majiayu000/dotnet-guidelines

---


# IMPORTANT Server Guidelines

- ALWAYS Use Primary Constructors for classes.
- ALWAYS Prefer `record` types for immutable data structures.
- NEVER mix multiple classes or DTOs in a single file, even if they are small. Filename ALWAYS matches the class or DTO name, for example `UserDto.cs` for a `UserDto` class.
- Private fields should NOT be prefixed with `_` (e.g., `repository` not `_repository`).
- Add (.) to the end of all server-side log messages.
- Use `string?` over `string` for nullable strings.
- Use `var` for local variables when type is obvious.
- Don't use Regions in code files.
- Use Collection initializers for collections: instead of `new List<string>()`, use `new() { "item1", "item2" }`, and instead of `list.ToArray()` use `[.. list]`.
- Use Anonymous function static: instead of `list.Select(x => new Dto(x.SameProperty))`, use `list.Select(static x => new Dto(x.SameProperty))`.
- ALWAYS use `sealed` accessor for classes or records if not intended for inheritance.
- ALWAYS use `internal` accessor for internal classes or records.
- NEVER inject or create `HttpClient` and `IHttpClientFactory`, instead use the `IRestClient` interface.
- NEVER register services directly in `IServiceCollection`. Instead, use the `ITransientService`, `IScopedService`, or `ISingletonService` interfaces to register services with the appropriate lifetimes.
- ALWAYS use `ILogger` with Structured logging to log, no string interpolation and no other logging methods.
- ALWAYS use cancellation tokens for asynchronous methods.
- ALWAYS use `IMemoryCore` for time-based in-memory caching, NEVER use `IMemoryCache`.
- ALWAYS use Data Transfer Objects (DTO) for API communication, validated with attributes.
- ALWAYS use `x` as a parameter name in lambdas and anonymous functions.
- If any backend changes are made, run `dotnet build` in the root and ensure no build errors for the entire solution.

## Code Organization Principles

### Avoid Unnecessary Wrapper Methods

**Rule**: Do NOT create wrapper methods for specific cases that simply call another method with fixed parameters. Call the base method directly instead.

**Example - DON'T**:

```csharp
// ❌ Don't create this wrapper method for a single use case:
public async Task<int> CreateAgentHistoryClearedMessageAsync(int sessionId)
{
    var request = new CreateMessageRequest(
        Type: MessageType.System,
        Content: "Agent history has been cleared",
        Status: MessageStatus.Done
    );
    return await CreateMessageAsync(sessionId, request);
}
```

**Example - DO**:

```csharp
// ✅ Instead, call CreateMessageAsync directly where needed:
await messageService.CreateMessageAsync(
    sessionId,
    new CreateMessageRequest(
        MessageType.System,
        "Agent history has been cleared",
        MessageStatus.Done
    )
);
```

**When to create a helper method**:

- When there's complex logic beyond just parameter mapping
- When the same combination is used in multiple places (3+ times)
- When the method provides meaningful abstraction or validation