Roslynator

Roslynator

Trigger On

• the repo uses or wants Roslynator.Analyzers
• the team wants Roslynator CLI or extra Roslyn-based rules
• the user asks about C# linting, static analysis, code cleanup, or unused code

Value

• produce a concrete project delta: code, docs, config, tests, CI, or review artifact
• reduce ambiguity through explicit planning, verification, and final validation skills
• leave reusable project context so future tasks are faster and safer

Do Not Use For

• repos that already have overlapping analyzer packs with no consolidation plan
• formatting-only work when the repo already standardized on dotnet format or CSharpier

Inputs

• the nearest AGENTS.md
• current analyzer packages
• .editorconfig

Quick Start

1. Read the nearest AGENTS.md and confirm scope and constraints. 2. Run this skill's Workflow through the Ralph Loop until outcomes are acceptable. 3. Return the Required Result Format with concrete artifacts and verification evidence.

Workflow

1. Prefer the NuGet analyzer packages for build-enforced checks. 2. Use the CLI when the repo needs one of these flows explicitly:

• analyze
• fix
• find-unused
• format

3. Build first when Roslynator needs compiled context. 4. Configure rule severity and Roslynator behavior in .editorconfig. 5. Avoid duplicating the same rules across multiple analyzer packs without a severity plan. 6. Treat CLI auto-fix as a controlled change:

• run it on a bounded target first
• rebuild
• rerun tests

Bootstrap When Missing

If Roslynator is not configured yet:

1. Detect current state:

• rg -n "Roslynator\\.Analyzers" -g '*.csproj' .
• rg --files -g '.config/dotnet-tools.json'
• dotnet tool list --local
• dotnet tool list --global
• command -v roslynator

2. Choose the install path deliberately:

• analyzer package: dotnet add PROJECT.csproj package Roslynator.Analyzers
• optional CLI: dotnet new tool-manifest (if missing) and dotnet tool install roslynator.dotnet.cli

3. Configure ownership in root .editorconfig so Roslynator does not fight SDK analyzers, StyleCop, or Meziantou. 4. If the CLI is adopted, add exact commands in AGENTS.md and CI, such as:

• dotnet tool run roslynator analyze SOLUTION_OR_PROJECT
• dotnet tool run roslynator fix SOLUTION_OR_PROJECT

5. Run dotnet build SOLUTION_OR_PROJECT and the selected Roslynator command, then return status: configured or status: improved. 6. If the repo wants only the current analyzer baseline and no Roslynator-specific CLI workflow, return status: not_applicable.

Deliver

• Roslynator package or CLI setup that fits the repo
• explicit ownership of rule severity
• repeatable commands for analyze, fix, or unused-code workflows when the repo adopts them

Validate

• Roslynator adds value beyond the current analyzer baseline
• CI commands remain reviewable and reproducible
• the repo is not confusing Roslynator CLI with the analyzer package itself

Ralph Loop

Use the Ralph Loop for every task, including docs, architecture, testing, and tooling work.

1. Plan first (mandatory):

• analyze current state
• define target outcome, constraints, and risks
• write a detailed execution plan
• list final validation skills to run at the end, with order and reason

2. Execute one planned step and produce a concrete delta. 3. Review the result and capture findings with actionable next fixes. 4. Apply fixes in small batches and rerun the relevant checks or review steps. 5. Update the plan after each iteration. 6. Repeat until outcomes are acceptable or only explicit exceptions remain. 7. If a dependency is missing, bootstrap it or return status: not_applicable with explicit reason and fallback path.

Required Result Format

• status: complete | clean | improved | configured | not_applicable | blocked
• plan: concise plan and current iteration step
• actions_taken: concrete changes made
• validation_skills: final skills run, or skipped with reasons
• verification: commands, checks, or review evidence summary
• remaining: top unresolved items or none

For setup-only requests with no execution, return status: configured and exact next commands.

Load References

• references/rules.md
• references/config.md
• references/roslynator.md

Example Requests

• "Add Roslynator analyzers."
• "Use Roslynator CLI in CI."
• "Find unused code with Roslynator."
• "Auto-fix Roslynator issues in this solution."

Roslynator EditorConfig Configuration

This document provides .editorconfig settings for configuring Roslynator analyzers.

Basic Setup

Roslynator respects standard .editorconfig files. Place configuration in your solution's root .editorconfig or in nested .editorconfig files for directory-specific settings.

Rule Severity Configuration

Configure rule severity using the standard diagnostic severity format:

[*.cs]
# Syntax: dotnet_diagnostic.<rule_id>.severity = <severity>
# Severities: none, silent, suggestion, warning, error

# Example: Disable a rule
dotnet_diagnostic.RCS1090.severity = none

# Example: Elevate to warning
dotnet_diagnostic.RCS1163.severity = warning

# Example: Treat as error
dotnet_diagnostic.RCS1155.severity = error

Roslynator-Specific Options

Roslynator provides additional configuration options beyond severity:

[*.cs]
# Configure specific rule behavior
roslynator_accessibility_modifiers = explicit
roslynator_accessor_braces_style = single_line_when_expression_is_on_single_line
roslynator_array_creation_type_style = implicit_when_type_is_obvious
roslynator_arrow_token_new_line = before
roslynator_binary_operator_new_line = before
roslynator_blank_line_after_file_scoped_namespace_declaration = true
roslynator_blank_line_between_closing_brace_and_switch_section = false
roslynator_blank_line_between_single_line_accessors = false
roslynator_blank_line_between_using_directives = never
roslynator_block_braces_style = single_line_when_empty
roslynator_body_style = expression
roslynator_conditional_operator_condition_parentheses_style = include
roslynator_conditional_operator_new_line = before
roslynator_configure_await = true
roslynator_doc_comment_summary_style = multi_line
roslynator_empty_string_style = literal
roslynator_enum_flag_value_style = decimal_number
roslynator_enum_has_flag_style = method
roslynator_equals_token_new_line = before
roslynator_infinite_loop_style = while
roslynator_max_line_length = 140
roslynator_new_line_at_end_of_file = true
roslynator_new_line_before_while_in_do_statement = true
roslynator_null_check_style = pattern_matching
roslynator_null_conditional_operator_new_line = before
roslynator_object_creation_parentheses_style = include
roslynator_object_creation_type_style = implicit_when_type_is_obvious
roslynator_prefix_field_identifier_with_underscore = true
roslynator_suppress_unity_script_methods = true
roslynator_tab_length = 4
roslynator_trailing_comma_style = omit_when_single_line
roslynator_unity_code_analysis.enabled = false
roslynator_use_anonymous_function_or_method_group = method_group
roslynator_use_block_body_when_declaration_spans_over_multiple_lines = true
roslynator_use_block_body_when_expression_spans_over_multiple_lines = true
roslynator_use_collection_expression = true
roslynator_use_var = when_type_is_obvious
roslynator_use_var_instead_of_implicit_object_creation = false

Refactoring Configuration

Enable or disable specific refactorings:

[*.cs]
# Syntax: roslynator_refactoring.<id>.enabled = true|false

# Example: Disable "Add braces" refactoring
roslynator_refactoring.RR0002.enabled = false

# Example: Enable "Extract method" refactoring
roslynator_refactoring.RR0047.enabled = true

Compiler Diagnostic Configuration

Configure standard compiler diagnostics alongside Roslynator:

[*.cs]
# Syntax: roslynator_compiler_diagnostic.<id>.enabled = true|false

# Example: Include specific compiler diagnostics in analysis
roslynator_compiler_diagnostic.CS0162.enabled = true

Complete Configuration Templates

Minimal Strict Configuration

A minimal configuration that enforces important code quality rules:

# .editorconfig
root = true

[*.cs]
# Core code quality rules - elevate to warning
dotnet_diagnostic.RCS1155.severity = warning  # Use StringComparison
dotnet_diagnostic.RCS1163.severity = warning  # Unused parameter
dotnet_diagnostic.RCS1169.severity = warning  # Make field read-only
dotnet_diagnostic.RCS1213.severity = warning  # Remove unused member
dotnet_diagnostic.RCS1225.severity = warning  # Make class sealed
dotnet_diagnostic.RCS1210.severity = warning  # Return completed task

# Performance rules
dotnet_diagnostic.RCS1077.severity = warning  # Optimize LINQ
dotnet_diagnostic.RCS1080.severity = warning  # Use Count/Length

# Architecture rules
dotnet_diagnostic.RCS1102.severity = warning  # Make class static
dotnet_diagnostic.RCS1110.severity = warning  # Type inside namespace

# Disable noisy rules
dotnet_diagnostic.RCS1090.severity = none     # ConfigureAwait (if not library)
dotnet_diagnostic.RCS1036.severity = none     # Remove blank line

Library/Package Configuration

Configuration suitable for libraries distributed via NuGet:

# .editorconfig
root = true

[*.cs]
# API design rules - enforce strictly
dotnet_diagnostic.RCS1110.severity = error    # Type inside namespace
dotnet_diagnostic.RCS1194.severity = error    # Exception constructors
dotnet_diagnostic.RCS1203.severity = error    # AttributeUsage
dotnet_diagnostic.RCS1160.severity = error    # Abstract public constructors
dotnet_diagnostic.RCS1193.severity = error    # params modifier

# Async rules - important for libraries
dotnet_diagnostic.RCS1090.severity = warning  # ConfigureAwait
dotnet_diagnostic.RCS1210.severity = error    # Return completed task
dotnet_diagnostic.RCS1046.severity = warning  # Async suffix
dotnet_diagnostic.RCS1047.severity = warning  # Non-async suffix

# Documentation
dotnet_diagnostic.RCS1138.severity = warning  # Summary required
dotnet_diagnostic.RCS1139.severity = warning  # Summary element
dotnet_diagnostic.RCS1141.severity = warning  # param element
dotnet_diagnostic.RCS1142.severity = warning  # typeparam element
dotnet_diagnostic.RCS1263.severity = error    # Invalid doc reference

# Code quality
dotnet_diagnostic.RCS1155.severity = error    # StringComparison
dotnet_diagnostic.RCS1163.severity = warning  # Unused parameter
dotnet_diagnostic.RCS1169.severity = warning  # Read-only field
dotnet_diagnostic.RCS1213.severity = warning  # Unused member

# Roslynator options
roslynator_configure_await = true
roslynator_accessibility_modifiers = explicit
roslynator_prefix_field_identifier_with_underscore = true

Application Configuration

Configuration suitable for applications (not libraries):

# .editorconfig
root = true

[*.cs]
# Disable library-specific rules
dotnet_diagnostic.RCS1090.severity = none     # ConfigureAwait
dotnet_diagnostic.RCS1046.severity = none     # Async suffix

# Enable code quality
dotnet_diagnostic.RCS1155.severity = warning  # StringComparison
dotnet_diagnostic.RCS1163.severity = warning  # Unused parameter
dotnet_diagnostic.RCS1169.severity = warning  # Read-only field
dotnet_diagnostic.RCS1213.severity = warning  # Unused member
dotnet_diagnostic.RCS1225.severity = warning  # Sealed class
dotnet_diagnostic.RCS1102.severity = warning  # Static class

# Performance
dotnet_diagnostic.RCS1077.severity = warning  # Optimize LINQ
dotnet_diagnostic.RCS1080.severity = warning  # Count/Length
dotnet_diagnostic.RCS1197.severity = warning  # StringBuilder
dotnet_diagnostic.RCS1235.severity = warning  # Optimize method

# Simplification
dotnet_diagnostic.RCS1049.severity = suggestion
dotnet_diagnostic.RCS1058.severity = suggestion
dotnet_diagnostic.RCS1068.severity = suggestion
dotnet_diagnostic.RCS1084.severity = suggestion

# Roslynator options
roslynator_configure_await = false
roslynator_use_var = when_type_is_obvious
roslynator_object_creation_type_style = implicit_when_type_is_obvious

Test Project Configuration

Configuration suitable for test projects:

# tests/.editorconfig
[*.cs]
# Relax some rules for test code
dotnet_diagnostic.RCS1163.severity = suggestion  # Unused parameter (common in tests)
dotnet_diagnostic.RCS1213.severity = suggestion  # Unused member (test helpers)
dotnet_diagnostic.RCS1225.severity = none        # Sealed (test classes often inherited)
dotnet_diagnostic.RCS1090.severity = none        # ConfigureAwait
dotnet_diagnostic.RCS1046.severity = none        # Async suffix

# Keep important rules
dotnet_diagnostic.RCS1155.severity = warning     # StringComparison
dotnet_diagnostic.RCS1077.severity = suggestion  # LINQ optimization

# Allow more flexibility
roslynator_use_var = always

Global Suppression

To suppress rules project-wide via GlobalSuppressions.cs:

// GlobalSuppressions.cs
using System.Diagnostics.CodeAnalysis;

[assembly: SuppressMessage("Roslynator", "RCS1090:Add call to 'ConfigureAwait'")]
[assembly: SuppressMessage("Roslynator", "RCS1036:Remove unnecessary blank line")]

Inline Suppression

Suppress rules inline with pragma directives:

#pragma warning disable RCS1163 // Unused parameter
public void Method(string unused)
#pragma warning restore RCS1163
{
    // ...
}

Or with attributes:

[SuppressMessage("Roslynator", "RCS1163:Unused parameter")]
public void Method(string unused)
{
    // ...
}

Combining with Other Analyzers

When using Roslynator alongside other analyzers (SDK analyzers, StyleCop, Meziantou), establish clear ownership:

[*.cs]
# Disable Roslynator formatting when using dotnet format or CSharpier
dotnet_diagnostic.RCS0001.severity = none
dotnet_diagnostic.RCS0002.severity = none
# ... other RCS0xxx rules

# Disable overlapping rules if StyleCop handles them
dotnet_diagnostic.RCS1018.severity = none  # Accessibility (SA1400)
dotnet_diagnostic.RCS1019.severity = none  # Modifier order (SA1206)

# Let SDK analyzers handle nullability
# Roslynator complements but doesn't replace CS8xxx rules

CLI-Specific Configuration

When using Roslynator CLI, additional options can be passed:

# Analyze with specific severity minimum
roslynator analyze Solution.sln --severity-level warning

# Fix with specific rules
roslynator fix Solution.sln --diagnostic-ids RCS1163,RCS1213

# Find unused code
roslynator find-unused Solution.sln

The CLI respects .editorconfig settings for rule configuration.

Further Reading

• Roslynator Configuration Documentation
• EditorConfig Specification
• .NET Code Analysis Configuration

Roslynator

Open/Free Status

• open source
• free to use

Install

Analyzer package:

dotnet add package Roslynator.Analyzers

Optional CLI:

dotnet tool install -g roslynator.dotnet.cli

Verify First

Before installing anything, check whether the repo already references the analyzer package or already has the CLI:

rg -n "Roslynator\\.Analyzers" -g '*.csproj' .
dotnet tool list --local
dotnet tool list --global
command -v roslynator

Requirements

• current Roslynator CLI requires a supported modern .NET SDK
• the official CLI docs currently list support for .NET SDK 7, 8, or 9 depending on Roslynator version

Important Distinction

• the CLI tool itself does not provide the analyzer rules by magic
• build-enforced diagnostics usually come from NuGet packages such as Roslynator.Analyzers
• the CLI is most useful for explicit analysis, fix, formatting, and unused-code workflows

Common Usage

dotnet build MySolution.sln -warnaserror
roslynator analyze MySolution.sln
roslynator fix MySolution.sln
roslynator format MySolution.sln
roslynator find-unused MySolution.sln
roslynator list-symbols MySolution.sln
roslynator lloc MySolution.sln

Useful CI-focused variation:

roslynator analyze MySolution.sln --severity-level warning

Useful scoping flags from the CLI:

• --projects PROJECT_NAME
• --ignored-projects PROJECT_NAME
• --include GLOB
• --exclude GLOB
• --verbosity LEVEL
• --properties NAME=VALUE

CI Fit

• prefer package-based analyzers as the primary gate
• use .editorconfig to configure rule severity
• keep CLI usage explicit if the repo adopts it
• use analyze for report-only flows and fix only in controlled local or pre-PR cleanup flows
• rebuild and retest after fix

Configuration

Roslynator configuration belongs in .editorconfig, for example:

[*.cs]
dotnet_analyzer_diagnostic.category-roslynator.severity = warning
dotnet_diagnostic.RCS1001.severity = none
dotnet_diagnostic.RCS1036.severity = error
roslynator_refactoring.add_braces.enabled = false

Exit Codes

• 0: success, or no diagnostics left for the current command
• 1: diagnostics found, or not all diagnostics fixed
• 2: error or execution canceled

When Not To Use

• when the repo already uses enough overlapping analyzers and does not want the extra rule surface
• when the team wants only build-integrated analyzer behavior and has no need for Roslynator CLI workflows

Sources

• Roslynator repository
• Roslynator.Analyzers package
• Roslynator CLI
• Roslynator configuration

Roslynator Rules Reference

This document covers commonly used Roslynator analyzer rules, organized by category.

Rule Naming Convention

Roslynator rules follow these prefixes:

• RCS0xxx - Formatting analyzers (from Roslynator.Formatting.Analyzers)
• RCS1xxx - Code analyzers (from Roslynator.Analyzers)
• RCS9xxx - Code analysis analyzers

Commonly Used Code Analyzers (RCS1xxx)

Simplification and Redundancy

Async and Threading

Design and Architecture

Formatting Analyzers (RCS0xxx)

These rules control code formatting and are part of Roslynator.Formatting.Analyzers:

High-Impact Rules for Code Quality

These rules have the highest impact on code quality and maintainability:

Must-Enable (Recommended as Warning or Error)

1. RCS1155 - Use StringComparison when comparing strings 2. RCS1210 - Return completed task instead of returning null 3. RCS1194 - Implement exception constructors 4. RCS1203 - Use AttributeUsageAttribute 5. RCS1110 - Declare type inside namespace 6. RCS1215 - Expression is always equal to true/false 7. RCS1263 - Invalid reference in a documentation comment 8. RCS1242 - Do not pass non-read-only struct by read-only reference 9. RCS1193 - Overriding member should not change 'params' modifier

Often Elevated to Warning

1. RCS1163 - Unused parameter 2. RCS1213 - Remove unused member declaration 3. RCS1169 - Make field read-only 4. RCS1102 - Make class static 5. RCS1225 - Make class sealed 6. RCS1077 - Optimize LINQ method call 7. RCS1080 - Use 'Count' or 'Length' property instead of 'Any' method

Performance-Related Rules

1. RCS1077 - Optimize LINQ method call 2. RCS1080 - Use 'Count' or 'Length' property instead of 'Any' method 3. RCS1096 - Convert 'HasFlag' call to bitwise operation 4. RCS1197 - Optimize StringBuilder.Append/AppendLine call 5. RCS1198 - Avoid unnecessary boxing of value type 6. RCS1235 - Optimize method call

Refactorings

Roslynator also provides refactorings (not analyzers) that can be invoked manually. These are not rule-based but are useful code transformations available through the IDE.

Common refactorings include:

• Add braces
• Extract method
• Inline method
• Introduce local variable
• Merge if statements
• Replace method group with lambda
• Split variable declaration
• Wrap in region
• And many more

Refactorings can be enabled/disabled in .editorconfig using roslynator_refactoring.<id>.enabled settings.

Further Reading

• Roslynator Analyzers Documentation
• Roslynator GitHub Repository
• Roslynator Configuration