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editorconfig

USE FOR: Configuring consistent C# coding styles, naming conventions, formatting rules, and Roslyn analyzer severity levels across editors and IDEs using .editorconfig files. DO NOT USE FOR: Runtime code behavior, NuGet package configuration, or MSBuild property settings that belong in Directory.Build.props.

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author
Tyler-R-Kendrick
version
1.0.0
displayName
EditorConfig for .NET

SKILL.md

EditorConfig for .NET

Overview

EditorConfig is a file-format specification that defines coding styles and formatting rules enforced by editors, IDEs, and build tooling. In .NET projects the .editorconfig file controls whitespace, indentation, naming conventions, code-style preferences, and Roslyn diagnostic severity levels. When EnforceCodeStyleInBuild is enabled in Directory.Build.props, violations reported by .editorconfig rules are promoted to build-time warnings or errors, making the file a first-class part of the project system.

A root .editorconfig placed at the repository top with root = true prevents editors from inheriting settings from parent directories. Nested .editorconfig files in subdirectories can override specific rules for tests, generated code, or legacy projects.

File Structure and Sections

Every .editorconfig begins with global settings, then adds per-glob overrides. Sections are declared with bracket-enclosed glob patterns.

ini
# .editorconfig
root = true

# Global defaults for all files
[*]
charset = utf-8
end_of_line = lf
indent_style = space
indent_size = 4
insert_final_newline = true
trim_trailing_whitespace = true
max_line_length = 120

# C# source files
[*.{cs,csx}]
indent_size = 4

# XML project files
[*.{csproj,props,targets}]
indent_size = 2

# JSON and YAML configuration
[*.{json,yml,yaml}]
indent_size = 2

# Markdown allows trailing whitespace for line breaks
[*.md]
trim_trailing_whitespace = false

# Generated files - relaxed rules
[**/obj/**.cs]
generated_code = true
dotnet_analyzer_diagnostic.severity = none

C# Code Style Rules

The .editorconfig controls expression-level preferences, pattern-matching style, null-checking, and using directive placement.

ini
[*.cs]
# 'var' preferences
csharp_style_var_for_built_in_types = true:suggestion
csharp_style_var_when_type_is_apparent = true:suggestion
csharp_style_var_elsewhere = true:suggestion

# Expression-bodied members
csharp_style_expression_bodied_methods = when_on_single_line:suggestion
csharp_style_expression_bodied_constructors = false:suggestion
csharp_style_expression_bodied_properties = true:suggestion
csharp_style_expression_bodied_accessors = true:suggestion
csharp_style_expression_bodied_lambdas = true:silent
csharp_style_expression_bodied_local_functions = false:silent

# Pattern matching
csharp_style_pattern_matching_over_is_with_cast_check = true:warning
csharp_style_pattern_matching_over_as_with_null_check = true:warning
csharp_style_prefer_switch_expression = true:suggestion
csharp_style_prefer_pattern_matching = true:suggestion
csharp_style_prefer_not_pattern = true:suggestion
csharp_style_prefer_extended_property_pattern = true:suggestion

# Null checking
csharp_style_throw_expression = true:suggestion
csharp_style_conditional_delegate_call = true:suggestion
dotnet_style_coalesce_expression = true:warning
dotnet_style_null_propagation = true:warning
csharp_style_prefer_null_check_over_type_check = true:suggestion

# Using directives
csharp_using_directive_placement = outside_namespace:warning
dotnet_sort_system_directives_first = true
dotnet_separate_import_directive_groups = false

# Namespace declarations
csharp_style_namespace_declarations = file_scoped:warning

# Primary constructors
csharp_style_prefer_primary_constructors = true:suggestion

C# Formatting Rules

Formatting rules control brace placement, spacing, and wrapping.

ini
[*.cs]
# New-line preferences
csharp_new_line_before_open_brace = all
csharp_new_line_before_else = true
csharp_new_line_before_catch = true
csharp_new_line_before_finally = true
csharp_new_line_before_members_in_object_initializers = true
csharp_new_line_before_members_in_anonymous_types = true
csharp_new_line_between_query_expression_clauses = true

# Indentation
csharp_indent_case_contents = true
csharp_indent_switch_labels = true
csharp_indent_labels = flush_left
csharp_indent_block_contents = true
csharp_indent_braces = false

# Spacing
csharp_space_after_cast = false
csharp_space_after_keywords_in_control_flow_statements = true
csharp_space_between_parentheses = false
csharp_space_before_colon_in_inheritance_clause = true
csharp_space_after_colon_in_inheritance_clause = true
csharp_space_around_binary_operators = before_and_after

# Wrapping
csharp_preserve_single_line_statements = false
csharp_preserve_single_line_blocks = true

Naming Conventions

Naming rules enforce PascalCase for public members, camelCase with underscore prefix for private fields, and interface prefix rules.

ini
[*.cs]
# Symbol specifications
dotnet_naming_symbols.public_members.applicable_kinds = property, method, event, delegate
dotnet_naming_symbols.public_members.applicable_accessibilities = public, internal, protected, protected_internal

dotnet_naming_symbols.private_fields.applicable_kinds = field
dotnet_naming_symbols.private_fields.applicable_accessibilities = private, private_protected

dotnet_naming_symbols.interfaces.applicable_kinds = interface
dotnet_naming_symbols.interfaces.applicable_accessibilities = *

dotnet_naming_symbols.type_parameters.applicable_kinds = type_parameter
dotnet_naming_symbols.type_parameters.applicable_accessibilities = *

dotnet_naming_symbols.const_fields.applicable_kinds = field
dotnet_naming_symbols.const_fields.required_modifiers = const

dotnet_naming_symbols.async_methods.applicable_kinds = method
dotnet_naming_symbols.async_methods.required_modifiers = async

# Naming styles
dotnet_naming_style.pascal_case.capitalization = pascal_case
dotnet_naming_style.camel_case_underscore.capitalization = camel_case
dotnet_naming_style.camel_case_underscore.required_prefix = _
dotnet_naming_style.interface_prefix.capitalization = pascal_case
dotnet_naming_style.interface_prefix.required_prefix = I
dotnet_naming_style.type_parameter_prefix.capitalization = pascal_case
dotnet_naming_style.type_parameter_prefix.required_prefix = T
dotnet_naming_style.async_suffix.capitalization = pascal_case
dotnet_naming_style.async_suffix.required_suffix = Async

# Naming rules (ordered by priority)
dotnet_naming_rule.interfaces_must_begin_with_i.symbols = interfaces
dotnet_naming_rule.interfaces_must_begin_with_i.style = interface_prefix
dotnet_naming_rule.interfaces_must_begin_with_i.severity = error

dotnet_naming_rule.type_parameters_must_begin_with_t.symbols = type_parameters
dotnet_naming_rule.type_parameters_must_begin_with_t.style = type_parameter_prefix
dotnet_naming_rule.type_parameters_must_begin_with_t.severity = error

dotnet_naming_rule.private_fields_camel_case.symbols = private_fields
dotnet_naming_rule.private_fields_camel_case.style = camel_case_underscore
dotnet_naming_rule.private_fields_camel_case.severity = warning

dotnet_naming_rule.const_fields_pascal_case.symbols = const_fields
dotnet_naming_rule.const_fields_pascal_case.style = pascal_case
dotnet_naming_rule.const_fields_pascal_case.severity = warning

dotnet_naming_rule.async_methods_must_end_with_async.symbols = async_methods
dotnet_naming_rule.async_methods_must_end_with_async.style = async_suffix
dotnet_naming_rule.async_methods_must_end_with_async.severity = suggestion

dotnet_naming_rule.public_members_pascal_case.symbols = public_members
dotnet_naming_rule.public_members_pascal_case.style = pascal_case
dotnet_naming_rule.public_members_pascal_case.severity = warning

Analyzer Severity Configuration

Control Roslyn analyzer diagnostic severity directly in .editorconfig instead of using #pragma directives or .globalconfig.

ini
[*.cs]
# .NET analyzer defaults
dotnet_analyzer_diagnostic.category-Style.severity = warning
dotnet_analyzer_diagnostic.category-Design.severity = warning
dotnet_analyzer_diagnostic.category-Performance.severity = warning
dotnet_analyzer_diagnostic.category-Reliability.severity = warning
dotnet_analyzer_diagnostic.category-Security.severity = error

# Specific rule overrides
dotnet_diagnostic.CA1062.severity = warning      # Validate arguments of public methods
dotnet_diagnostic.CA1822.severity = suggestion    # Mark members as static
dotnet_diagnostic.CA2007.severity = none          # Do not directly await a Task (library-only)
dotnet_diagnostic.IDE0005.severity = warning      # Remove unnecessary usings
dotnet_diagnostic.IDE0055.severity = warning      # Fix formatting
dotnet_diagnostic.IDE0060.severity = warning      # Remove unused parameter
dotnet_diagnostic.IDE0090.severity = suggestion   # Simplify new expression
dotnet_diagnostic.CS8618.severity = warning       # Non-nullable field uninitialized

# Test projects - relax certain rules
[*Tests/**/*.cs]
dotnet_diagnostic.CA1707.severity = none          # Allow underscores in test method names
dotnet_diagnostic.CA1062.severity = none          # Test parameters do not need validation
dotnet_diagnostic.CA2007.severity = none

Severity Levels Reference

Severity Build Behavior Editor Behavior
error Fails the build Red squiggly underline
warning Build warning (error with TreatWarningsAsErrors) Green squiggly underline
suggestion Build info message Gray dots under first two chars
silent No build output Refactoring available on demand
none Rule completely disabled No analysis performed

Best Practices

  1. Place the root .editorconfig at the repository root with root = true to prevent accidental inheritance from user-profile or machine-level .editorconfig files that exist outside your repository.

  2. Set EnforceCodeStyleInBuild to true in Directory.Build.props so that code-style rules defined in .editorconfig are enforced during dotnet build, not only inside the IDE.

  3. Use severity level warning rather than error for style rules during initial adoption to avoid blocking builds while the team adjusts; escalate to error once the codebase is clean.

  4. Create a separate [*Tests/**/*.cs] section that relaxes rules like CA1707 and CA1062 because test methods conventionally use underscores in names and test parameters do not require null-guards.

  5. Define naming rules in priority order with explicit severity levels because .editorconfig naming rules are evaluated top-to-bottom and the first matching rule wins; place more specific rules (interfaces, type parameters) before general rules (public members).

  6. Pin csharp_style_namespace_declarations = file_scoped:warning to enforce file-scoped namespaces across the codebase and eliminate unnecessary indentation in every source file.

  7. Add generated_code = true and dotnet_analyzer_diagnostic.severity = none for obj and auto-generated file globs to prevent analyzers from reporting false positives on machine-generated code.

  8. Commit the .editorconfig to version control and review changes to it through pull requests to ensure the entire team agrees on style changes before they are enforced.

  9. Use dotnet_sort_system_directives_first = true with csharp_using_directive_placement = outside_namespace:warning for a consistent, predictable ordering of using directives across all files.

  10. Run dotnet format in CI as a verification step after configuring .editorconfig to catch formatting drift and ensure every committed file conforms to the declared style rules.

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