If your .NET library is meant for consumers using different .NET languages, choose a CLS-compliant public API as its baseline. Keep language-specific features where they provide real value to your intended users, but isolate and document those exceptions—and offer a compliant alternative when it makes sense. CLS rules govern the public contract, not private implementation details.
What CLS compliance means for a library
The Common Language Specification (CLS) defines a shared set of rules for generated assemblies so components can be consumed by other assemblies written in languages that support the CLS. Microsoft explains that compliance applies to a component’s public interface, not its private implementation. Microsoft’s language-independence guidance describes the public interface as the part that needs to follow the rules when designing a language-independent component.
That makes the choice about your published contract: signatures, types, and members exposed to callers. You do not need to redesign internal code merely because it uses a feature outside the CLS.
Choose based on who must consume the API
| Consideration | CLS-compliant public API | Language-specific public API |
|---|---|---|
| Consumer-language reach | Best when callers may use different .NET languages and compilers that support the CLS. | Narrows the shared surface for consumers whose language or compiler does not support the feature. |
| Fit for intended users | Favors a common contract across supported languages. | Can preserve features that materially serve the library’s expected consumers. |
| Exceptions and maintenance | Compliance can be declared and checked; alternatives can be exposed for exceptions. | Requires deliberate identification and documentation of non-compliant members and any corresponding compliant routes. |
These are design trade-offs, not a rule that every library must target every language. If the library has a known, narrow audience and a language-specific feature is important to that audience, using it may be reasonable. If cross-language use is a genuine requirement, avoid making that feature a barrier across the whole public contract where you can confine it to particular members.
Windows Errors? Fix Them Before They Spread
Repair common Windows errors and clear accumulated junk for a smoother, more stable PC - no reinstall needed.Free scan · no reinstallOutdated Drivers Are Slowing You Down
One free scan finds every outdated or missing driver and matches the right update for your exact hardware.Free scan · exact hardware match#1 Best Overall
A practical middle path: compliant core, deliberate extensions
You can keep the main API usable across CLS-supporting languages while exposing a language-specific extension for consumers who need it. For example, a compliant member can provide the shared operation, while a separately marked member exposes an additional capability that is not CLS-compliant. Name and document the relationship so consumers can tell which route to use.
Do not assume every non-compliant member needs a duplicate. Provide an equivalent compliant alternative when it is useful to the intended audience and the operation can be represented appropriately. Microsoft’s guidance recommends identifying exceptions and their compliant alternatives in product documentation.
Declare and review compliance in .NET
- Declare the intended assembly contract. If you intend the public surface to be CLS-compliant, add
[assembly: CLSCompliant(true)]. The attribute declares intent; it does not change signatures or make an incompatible API compliant. See Microsoft’s CLSCompliantAttribute documentation. - Resolve the resulting warnings. Review public types and members flagged as non-compliant. Microsoft’s examples include
UInt32as a type outside the CLS; treat such examples as prompts to review the public surface, not a complete catalog of all CLS rules. - Mark intentional exceptions. Apply
[CLSCompliant(false)]to a deliberately non-compliant public type or member, and document a compliant alternative when one is provided. The same consideration applies to interfaces: Microsoft notes that a CLS-compliant interface cannot include a non-compliant method. - Check the analyzer configuration. CA1014, “Mark assemblies with CLSCompliantAttribute,” is a useful design signal when enabled. Microsoft’s current rule table says it is not enabled by default in .NET 10, so check your project’s analyzer configuration rather than assuming the rule will run automatically. See Microsoft’s CA1014 documentation.
When a language-specific API is the better choice
Choose a language-specific public feature when it materially improves the library for its defined consumers and broader language interoperability is not a requirement for that part of the API. Keep the exception as narrow as practical: a single member or type is easier for consumers to understand than an entire surface with undocumented restrictions. If requirements change later, a compliant alternative gives more callers a route without forcing you to remove the specialized API.
Quick Recap
Rank #4
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.
Do these 3 things before closing this tab:
1Repair Windows errors before they cause bigger problems2Scan for outdated or missing drivers - takes under a minute3Clear out junk files and repair common Windows errors
