C#/.NET Code Review Skill

C#/.NET Code Review

Review C# code changes for best practices, modern patterns, and maintainability.

Getting Changes to Review

Determine what the user wants reviewed, then get the diffs:

# Last N commits
git --no-pager diff HEAD~3..HEAD -- '*.cs'

# Since a specific commit
git --no-pager diff abcd1234..HEAD -- '*.cs'

# Between two commits
git --no-pager diff abcd1234..2345bcde -- '*.cs'

# Staged changes
git --no-pager diff --cached -- '*.cs'

# Unstaged changes
git --no-pager diff -- '*.cs'

For full file context when needed:

git --no-pager show HEAD:path/to/file.cs

Review Checklist

Review changes against these principles:

Modern C# 14/.NET 10

[ ] Use collection expressions [1, 2, 3] instead of new List<int> { 1, 2, 3 }
[ ] Use primary constructors where appropriate
[ ] Use file-scoped namespaces
[ ] Use pattern matching over type checks and casts
[ ] Use switch expressions where applicable

DTOs and Records

[ ] DTOs should be record types, not classes
[ ] Records should be immutable (use init properties or positional parameters)
[ ] Records should use primary constructors
[ ] Collections in records should be ImmutableList<T>/ImmutableDictionary<K,V> or IReadOnlyList<T>/IReadOnlyDictionary<K,V>
[ ] DTOs/Records should have minimal behavior (no business logic)

SOLID Principles

[ ] Single Responsibility: Each class has one reason to change
[ ] Open-Closed: Open for extension, closed for modification
[ ] Dependency Inversion: Depend on interfaces, not concrete implementations
[ ] Always question inheritance — prefer composition

Error Handling

[ ] Do not use null for control flow
[ ] Avoid redundant null checks—let errors bubble up
[ ] Avoid unnecessary try/catch blocks—don't swallow exceptions
[ ] Use result types or exceptions appropriately for the context

Code Smells

[ ] Avoid primitive obsession (use domain types)
[ ] No new Newtonsoft.Json references — use System.Text.Json
[ ] No new Reflection-based code
[ ] Use HostApplicationBuilder not legacy IHostBuilder

Documentation

[ ] Public and internal classes/members are documented
[ ] Comments explain why, not what

Dependency Injection

[ ] If using DI, consider: could this be a service?
[ ] Services should depend on interfaces

Testing

[ ] Tests use FluentAssertions/AwesomeAssertions/Shouldly if present in project
[ ] Do not add unnecessary Arrange-Act-Assert comments

Output Format

For each issue found:

### [Category]: Brief description

**File**: `path/to/file.cs` (lines X-Y)

**Issue**: Explain what's wrong and why it matters.

**Suggestion**:
```cs
// Recommended code


Prioritize issues by impact: correctness > security > maintainability > style.

Agent Skills: C#/.NET Code Review

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