Recommended Free Tools
Target the Common Language Specification (CLS) when you want your library’s public API to work across .NET languages that support the CLS. It is an interoperability choice, not a requirement for every library: CLS rules apply to the public interface, not private implementation. If your API intentionally exposes features outside the CLS, identify those exceptions and offer compliant alternatives where practical.
What CLS compliance means for a library
The CLS is a subset of .NET features intended to let components written in different CLS-supporting languages interact. A library that declares CLS compliance is signaling that its public API follows those shared rules; it is not promising that every .NET language supports every .NET feature.
Microsoft states: “The rules for CLS compliance apply only to a component’s public interface, not to its private implementation.” That means you can use non-CLS features internally without making the library’s API noncompliant, provided those features do not leak into its exposed surface. See Microsoft Learn’s overview of language independence and language-independent components.
When to choose CLS compliance
Choose it for a broad or cross-language audience
Mark the library CLS-compliant when consumers may use different .NET languages, or when cross-language accessibility is an explicit compatibility goal. This makes the intended reach of the API clear and gives compiler checks a basis for identifying incompatible public signatures.
Free tools Windows power users keep installed
One-click scans. No signup required.
#1 Best Overall
Consider an exception for a narrower audience
If you know your consumers and a non-CLS feature materially improves the API for them, you may choose to expose it. Be clear that the affected API is not CLS-compliant; do not present the entire public surface as compliant without identifying the exception. Where feasible, provide another member or type that gives CLS-supporting consumers equivalent utility.
The decision comes down to audience, the value of the feature, whether a compliant alternative is practical, and whether you can keep exceptions documented and consistent.
How to declare and check compliance
-
Add
[assembly: CLSCompliant(true)]to declare that the assembly’s public API is intended to comply. -
Review public and protected types and member signatures for features outside the CLS. Private implementation details do not need to comply.
Quick wins for a faster PC:
Repair Windows errors before they cause bigger problemsFix Now →Scan for outdated or missing drivers - takes under a minuteDriver Scan →Special offer. See more information about Outbyte and uninstall instructions. Please review EULA and Privacy policy. -
For an intentional exposed exception, mark the relevant type or member with
[CLSCompliant(false)]. Document the exception and point readers to its compliant alternative, if one exists. -
Treat compiler warnings as design-review signals: correct unintended violations or make deliberate exceptions explicit. Individual compilers may enforce some CLS rules even when the attribute is absent.
Rank #4
CLSCompliantAttribute can be applied to assemblies, modules, types, and members. Its value is inherited by contained elements and can be overridden for exposed exceptions. Although the attribute usage allows other targets, Microsoft says applications to parameters, generic parameters, and return values are ignored in practice; mark the containing member instead. See the CLSCompliantAttribute API reference.
What the assembly attribute does—and does not do
The attribute declares compliance intent and enables compiler warnings for noncompliant public signatures presumed compliant. It does not make an incompatible signature compatible by itself; API design and review still matter.
The Tool Desk
Outbyte PC Repair FREERepair Windows errors before they cause bigger problemsFix Now →Outbyte Driver Updater FREEScan for outdated or missing drivers - takes under a minuteDriver Scan →Microsoft’s CA1014 code-analysis guidance says, “Good design dictates that all assemblies explicitly indicate CLS compliance with CLSCompliantAttribute.” This is a design recommendation grounded in cross-language clarity, not a universal requirement that every library restrict its API. See Microsoft Learn’s CA1014 guidance.
A quick decision checklist
-
Do you want consumers in different CLS-supporting .NET languages to use the public API? Prefer declaring and checking CLS compliance.
-
Does a non-CLS feature provide important value to your known audience? You can expose it deliberately, but label the affected API and document its limits.
-
Can you offer a compliant alternative without making the API confusing or costly to maintain? If so, provide it and explain the relationship.
Special offer. See more information about Outbyte and uninstall instructions. Please review EULA and Privacy policy. -
Is a feature used only inside the library? CLS rules do not require changing private implementation solely for compliance.
Quick Recap
SaleBestseller No. 2SaleBestseller No. 3
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
