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Overview of .NET source code analysis

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.NET compiler platform (Roslyn) analyzers inspect your C# or Visual Basic code for code quality and style issues. Starting in .NET 5, these analyzers are included with the .NET SDK and you don't need to install them separately. If your project targets .NET 5 or later, code analysis is enabled by default. If your project targets a different .NET implementation, for example, .NET Core, .NET Standard, or .NET Framework, you must manually enable code analysis by setting the EnableNETAnalyzers property to true.

If you don't want to move to the .NET 5+ SDK, have a non-SDK-style .NET Framework project, or prefer a NuGet package-based model, the analyzers are also available in the Microsoft.CodeAnalysis.NetAnalyzers NuGet package. You might prefer a package-based model for on-demand version updates.

Note

.NET analyzers are target-framework agnostic. That is, your project does not need to target a specific .NET implementation. The analyzers work for projects that target .NET 5+ as well as earlier .NET versions, such as .NET Core 3.1 and .NET Framework 4.7.2. However, to enable code analysis using the EnableNETAnalyzers property, your project must reference a project SDK.

If rule violations are found by an analyzer, they're reported as a suggestion, warning, or error, depending on how each rule is configured. Code analysis violations appear with the prefix "CA" or "IDE" to differentiate them from compiler errors.

Code quality analysis

Code quality analysis ("CAxxxx") rules inspect your C# or Visual Basic code for security, performance, design and other issues. Analysis is enabled, by default, for projects that target .NET 5 or later. You can enable code analysis on projects that target earlier .NET versions by setting the EnableNETAnalyzers property to true. You can also disable code analysis for your project by setting EnableNETAnalyzers to false.

Tip

If you're using Visual Studio, many analyzer rules have associated code fixes that you can apply to correct the problem. Code fixes are shown in the light bulb icon menu.

Enabled rules

The following rules are enabled, by default, as errors or warnings in .NET 9. Additional rules are enabled as suggestions.

Diagnostic ID Category Severity Version added Description
CA1416 Interoperability Warning .NET 5 Validate platform compatibility
CA1417 Interoperability Warning .NET 5 Do not use OutAttribute on string parameters for P/Invokes
CA1418 Interoperability Warning .NET 6 Use valid platform string
CA1420 Interoperability Warning .NET 7 Using features that require runtime marshalling when it's disabled will result in run-time exceptions
CA1422 Interoperability Warning .NET 7 Validate platform compatibility
CA1831 Performance Warning .NET 5 Use AsSpan instead of range-based indexers for string when appropriate
CA1856 Performance Error .NET 8 Incorrect usage of ConstantExpected attribute
CA1857 Performance Warning .NET 8 A constant is expected for the parameter
CA2013 Reliability Warning .NET 5 Do not use ReferenceEquals with value types
CA2014 Reliability Warning .NET 5 Do not use stackalloc in loops
CA2015 Reliability Warning .NET 5 Do not define finalizers for types derived from MemoryManager<T>
CA2017 Reliability Warning .NET 6 Parameter count mismatch
CA2018 Reliability Warning .NET 6 The count argument to Buffer.BlockCopy should specify the number of bytes to copy
CA2021 Reliability Warning .NET 8 Do not call Enumerable.Cast<T> or Enumerable.OfType<T> with incompatible types
CA2022 Reliability Warning .NET 9 Avoid inexact read with Stream.Read
CA2200 Usage Warning .NET 5 Rethrow to preserve stack details
CA2247 Usage Warning .NET 5 Argument passed to TaskCompletionSource constructor should be TaskCreationOptions enum instead of TaskContinuationOptions
CA2252 Usage Error .NET 6 Opt in to preview features
CA2255 Usage Warning .NET 6 The ModuleInitializer attribute should not be used in libraries
CA2256 Usage Warning .NET 6 All members declared in parent interfaces must have an implementation in a DynamicInterfaceCastableImplementation-attributed interface
CA2257 Usage Warning .NET 6 Members defined on an interface with the DynamicInterfaceCastableImplementationAttribute should be static
CA2258 Usage Warning .NET 6 Providing a DynamicInterfaceCastableImplementation interface in Visual Basic is unsupported
CA2259 Usage Warning .NET 7 ThreadStatic only affects static fields
CA2260 Usage Warning .NET 7 Use correct type parameter
CA2261 Usage Warning .NET 8 Do not use ConfigureAwaitOptions.SuppressThrowing with Task<TResult>
CA2264 Usage Warning .NET 9 Do not pass a non-nullable value to ArgumentNullException.ThrowIfNull
CA2265 Usage Warning .NET 9 Do not compare Span<T> to null or default

You can change the severity of these rules to disable them or elevate them to errors. You can also enable more rules.

Enable additional rules

Analysis mode refers to a predefined code analysis configuration where none, some, or all rules are enabled. In the default analysis mode (Default), only a small number of rules are enabled as build warnings. You can change the analysis mode for your project by setting the <AnalysisMode> property in the project file. The allowable values are:

Value Description
None All rules are disabled. You can selectively opt in to individual rules to enable them.
Default Default mode, where certain rules are enabled as build warnings, certain rules are enabled as Visual Studio IDE suggestions, and the remainder are disabled.
Minimum More aggressive mode than Default mode. Certain suggestions that are highly recommended for build enforcement are enabled as build warnings. To see which rules this includes, inspect the %ProgramFiles%/dotnet/sdk/[version]/Sdks/Microsoft.NET.Sdk/analyzers/build/config/analysislevel_[level]_minimum.editorconfig file.
Recommended More aggressive mode than Minimum mode, where more rules are enabled as build warnings. To see which rules this includes, inspect the %ProgramFiles%/dotnet/sdk/[version]/Sdks/Microsoft.NET.Sdk/analyzers/build/config/analysislevel_[level]_recommended.editorconfig file.
All All rules are enabled as build warnings*. You can selectively opt out of individual rules to disable them.

* The following rules are not enabled by setting AnalysisMode to All or by setting AnalysisLevel to latest-all: CA1017, CA1045, CA1005, CA1014, CA1060, CA1021, and the code metrics analyzer rules (CA1501, CA1502, CA1505, CA1506, and CA1509). These legacy rules might be deprecated in a future version. However, you can still enable them individually using a dotnet_diagnostic.CAxxxx.severity = <severity> entry.

You can also omit <AnalysisMode> in favor of a compound value for the <AnalysisLevel> property. For example, the following value enables the recommended set of rules for the latest release: <AnalysisLevel>latest-Recommended</AnalysisLevel>. For more information, see AnalysisLevel.

To find the default severity for each available rule and whether or not the rule is enabled in Default analysis mode, see the full list of rules.

Treat warnings as errors

If you use the -warnaserror flag when you build your projects, all code analysis warnings are also treated as errors. If you do not want code quality warnings (CAxxxx) to be treated as errors in presence of -warnaserror, you can set the CodeAnalysisTreatWarningsAsErrors MSBuild property to false in your project file.

<PropertyGroup>
  <CodeAnalysisTreatWarningsAsErrors>false</CodeAnalysisTreatWarningsAsErrors>
</PropertyGroup>

You'll still see any code analysis warnings, but they won't break your build.

Latest updates

By default, you'll get the latest code analysis rules and default rule severities as you upgrade to newer versions of the .NET SDK. If you don't want this behavior, for example, if you want to ensure that no new rules are enabled or disabled, you can override it in one of the following ways:

  • Set the AnalysisLevel MSBuild property to a specific value to lock the warnings to that set. When you upgrade to a newer SDK, you'll still get bug fixes for those warnings, but no new warnings will be enabled and no existing warnings will be disabled. For example, to lock the set of rules to those that ship with version 8.0 of the .NET SDK, add the following entry to your project file.

    <PropertyGroup>
  <AnalysisLevel>8.0</AnalysisLevel>
</PropertyGroup>

    Tip

    The default value for the AnalysisLevel property is latest, which means you always get the latest code analysis rules as you move to newer versions of the .NET SDK.

    For more information, and to see a list of possible values, see AnalysisLevel.

  • Install the Microsoft.CodeAnalysis.NetAnalyzers NuGet package to decouple rule updates from .NET SDK updates. For projects that target .NET 5+, installing the package turns off the built-in SDK analyzers. You'll get a build warning if the SDK contains a newer analyzer assembly version than that of the NuGet package. To disable the warning, set the _SkipUpgradeNetAnalyzersNuGetWarning property to true.

    Note

    If you install the Microsoft.CodeAnalysis.NetAnalyzers NuGet package, you should not add the EnableNETAnalyzers property to either your project file or a Directory.Build.props file. When the NuGet package is installed and the EnableNETAnalyzers property is set to true, a build warning is generated.

Code-style analysis

Code-style analysis ("IDExxxx") rules enable you to define and maintain consistent code style in your codebase. The default enablement settings are:

  • Command-line build: Code-style analysis is disabled, by default, for all .NET projects on command-line builds.

    You can enable code-style analysis on build, both at the command line and inside Visual Studio. Code style violations appear as warnings or errors with an "IDE" prefix. This enables you to enforce consistent code styles at build time.

  • Visual Studio: Code-style analysis is enabled, by default, for all .NET projects inside Visual Studio as code refactoring quick actions.

For a full list of code-style analysis rules, see Code style rules.

Enable on build

You can enable code-style analysis when building from the command-line and in Visual Studio. (However, for performance reasons, a handful of code-style rules will still apply only in the Visual Studio IDE.)

Follow these steps to enable code-style analysis on build:

  1. Set the MSBuild property EnforceCodeStyleInBuild to true.

  2. In an .editorconfig file, configure each "IDE" code style rule that you wish to run on build as a warning or an error. For example:

    [*.{cs,vb}]
# IDE0040: Accessibility modifiers required (escalated to a build warning)
dotnet_diagnostic.IDE0040.severity = warning

    Tip

    Starting in .NET 9, you can also use the option format to specify a severity and have it be respected at build time. For example:

    [*.{cs,vb}]
# IDE0040: Accessibility modifiers required (escalated to a build warning)
dotnet_style_require_accessibility_modifiers = always:warning

    Alternatively, you can configure an entire category to be a warning or error, by default, and then selectively turn off rules in that category that you don't want to run on build. For example:

    [*.{cs,vb}]

# Default severity for analyzer diagnostics with category 'Style' (escalated to build warnings)
dotnet_analyzer_diagnostic.category-Style.severity = warning

# IDE0040: Accessibility modifiers required (disabled on build)
dotnet_diagnostic.IDE0040.severity = silent

Suppress a warning

One way to suppress a rule violation is to set the severity option for that rule ID to none in an EditorConfig file. For example:

dotnet_diagnostic.CA1822.severity = none

For more information and other ways to suppress warnings, see How to suppress code analysis warnings.

Third-party analyzers

In addition to the official .NET analyzers, you can also install third party analyzers, such as StyleCop, Roslynator, XUnit Analyzers, and Sonar Analyzer.

See also