csharp-coding-standards

name	csharp-coding-standards
description	**REVIEW/FORMAT SKILL** — Enforce official Microsoft C# coding conventions for naming, style, and language usage. WHEN: "review C# code", "check coding standards", "format C# code", "enforce C# conventions", "naming conventions", "C# style check", "code review", "check csharp standards". INVOKES: grep, view, edit.

C# Coding Standards

Enforces Microsoft's official C# coding conventions and identifier naming rules when reviewing or formatting C# code.

User Input

$ARGUMENTS

You MUST consider the user input before proceeding (if not empty).

Modes

Review Mode (default)

When the user asks to review C# code, scan for violations and report them grouped by category. Do not modify files unless asked.

Format Mode

When the user asks to format or fix C# code, apply corrections directly using the edit tool.

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Rules

1 · Naming Conventions

Element	Casing	Prefix	Example
Class, struct, record, delegate, enum	PascalCase	—	DataService
Interface	PascalCase	I	IWorkerQueue
Public field, property, event, method, local function	PascalCase	—	StartProcessing()
Private / internal field	camelCase	_	_workerQueue
Private / internal static field	camelCase	s_	s_workerQueue
Thread-static field	camelCase	t_	t_timeSpan
Local variable, method parameter	camelCase	—	isValid
Constant (field or local)	PascalCase	—	MaxRetryCount
Generic type parameter	PascalCase	T	TSession
Attribute type	PascalCase	— (suffix Attribute)	ObsoleteAttribute
Enum (non-flags)	Singular noun	—	Color
Enum (flags)	Plural noun	—	FilePermissions
Record primary constructor params	PascalCase	—	Person(string FirstName)
Class/struct primary constructor params	camelCase	—	DataService(ILogger logger)

Additional rules:

• Prefer clarity over brevity. Use meaningful, descriptive names.
• Avoid abbreviations except widely known ones (Id, Url, Html).
• Avoid single-letter names except simple loop counters.
• Never use two consecutive underscores (__).

2 · Type References

• Use language keywords, not runtime types: string not System.String, int not System.Int32.
• Prefer int over unsigned types unless domain-required.

3 · var Usage

• ✅ Use var when type is obvious from the right side (new, cast, literal).
• ✅ Use var in for loop variables.
• ✅ Use var for LINQ query results.
• ❌ Don't use var when type isn't apparent from the expression.
• ❌ Don't use var in foreach — use explicit element type.
• ❌ Never use var in place of dynamic.

4 · String Handling

• Use string interpolation ($"") for short concatenation.
• Use StringBuilder for loops or large text assembly.
• Prefer raw string literals ("""...""") over escape sequences / verbatim strings.
• Prefer expression-based interpolation over String.Format.

5 · Modern Constructs (prefer when applicable)

• Collection expressions: string[] vowels = ["a", "e", "i", "o", "u"];
• Func<> / Action<> over custom delegate types.
• using declarations (braceless) over try-finally for IDisposable.
• Target-typed new(): ExampleClass instance = new();
• Object initializers over sequential property assignment.
• required properties over constructor-forced initialization.
• File-scoped namespaces: namespace MyApp;
• Lambda event handlers for non-removable subscriptions.
• && / || (short-circuit) instead of & / | for boolean logic.

6 · Exception Handling

• Catch specific exception types, never bare System.Exception.
• Use using statements/declarations for IDisposable, not try-finally.
• Re-throw with throw; not throw ex;.

7 · Async

• Use async / await for I/O-bound operations.
• Use ConfigureAwait where appropriate.

8 · LINQ

• Use meaningful query variable names.
• Alias anonymous type properties with PascalCase.
• Align clauses under the from keyword.
• Place where before other clauses.
• Prefer multiple from over join for inner collections.

9 · Formatting & Layout

• 4 spaces indentation — no tabs.
• Allman braces — opening and closing brace each on own line.
• One statement per line. One declaration per line.
• Blank line between method/property definitions.
• Use parentheses to clarify operator precedence.
• Line break before binary operators when wrapping.
• using directives outside namespace declarations.

10 · Comments

• Single-line // comments only — avoid /* */.
• XML doc comments (///) for all public members.
• Comments on separate lines, not end-of-line.
• Begin with uppercase, end with period, space after //.

11 · Static Members

• Call via class name: ClassName.StaticMember.
• Never qualify base-class statics with a derived class name.

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Review Output Format

When reviewing, report violations as:

## C# Coding Standards Review

### ❌ Violations Found

**Naming** (Rule 1)
- `src/Foo.cs:12` — Private field `workerQueue` missing `_` prefix → `_workerQueue`

**var Usage** (Rule 3)
- `src/Bar.cs:45` — `var result = GetCount();` — type not obvious, use explicit `int`

### ✅ Compliant
- String handling
- Exception handling
- Formatting & layout

Omit compliant categories if violations exist in every category. Always show the violation count summary at the top.