ASP.NET Core API Versioning: Practical Strategies and Examples

# ASP.NET Core API Versioning: Practical Strategies and Examples API contracts often live longer than the code that implements them. Versioning gives clients a predictable way to continue using an older contract while a newer contract is introduced. ## Why version an API? Suppose an endpoint initially returns: ```json { "id": 10, "name": "Laptop" } ``` Later, the contract needs to change substantially. Existing mobile or external clients may not be ready to consume that new shape immediately. A versioned API can support the old and new contracts during the transition. ## Common versioning strategies ### URL path versioning A version can be represented directly in the URL: ```text /api/v1/products /api/v2/products ``` This is easy to discover and test. ### Query-string versioning Another option is: ```text /api/products?api-version=1.0 ``` This keeps the resource path stable while expressing the requested contract separately. ### Header-based versioning The client can request a version using a header. This keeps the URL clean but requires clients and tools to understand the versioning convention. ## When should you create a new version? Not every change requires a new API version. Adding a backward-compatible optional response property may not require one. Removing a property, changing its meaning, or altering required request behavior is more likely to be a breaking change. ## Keep versioning intentional Before introducing a new version, document: - What changed. - Which clients are affected. - How long the old version will remain supported. - How clients should migrate. ## Summary API versioning is mainly a contract-management strategy. Choose one clear convention, apply it consistently, document breaking changes, and avoid creating versions for changes that are safely backward compatible.

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