As your experience and knowledge of a system grow, change becomes inevitable. Your application requirements change, your bug fixes require code changes, and your APIs evolve. A key challenge in the software ecosystem is managing changes—especially when they concern APIs. Because you’re likely using APIs in multiple applications, you must document all updates and changes made to your APIs. This is where API versioning becomes crucial.

API versioning is a system of managing API changes so that these changes don’t negatively affect consumers or clients. Versioning defines a clear strategy for managing changes and reflecting them in your API structure. However, to be effective, you must communicate your API versioning strategy with all API consumers—not just internal ones.

API versioning is especially important when it comes to breaking changes. You don’t want to break existing applications when you make changes to your API. Therefore, you need to communicate any potential breaking changes when you up-version. Breaking changes include:

• Changing an endpoint’s response format
• Removing an API endpoint
• Changing the behavior of API filters or options
• Changing the expected request format for an API endpoint

If you push changes without notifying your API consumers, parts of their applications could malfunction or fail. Even a minor change like adding a new field to an API response could cause an issue for consumers who store cached versions of API responses. A new response format can confuse their tooling.

It’s one thing to be familiar with API versioning, but it’s another to implement. This article discusses how API versioning works and highlights its importance for API developers and consumers, exploring five strategies and best practices for using API versioning.

Smoothly Managing API Versions

Without implementing versioning best practices, your API consumers may encounter broken features, as they may be unaware of changes that might affect the relevant endpoints for their services.

You can improve the reliability and stability of your API for consumers by introducing an API contract. The API contract is an agreement between the API producer and consumer that describes how the API functions. If you build and maintain a consistent API contract, you can ensure API updates don’t render consumers’ applications inoperable.

5 API Versioning Best Practices

To ensure API stability, you need to ensure your API contract stays intact. To do so, follow these five API versioning best practices.

1. Enforce Backward Compatibility

When working with APIs, it’s important to enforce backward compatibility

API consumers lose business revenue every time they have to upgrade their application to comply with a new API contract. Too many breaking changes in a short period will likely prompt your API consumers to begin looking for a more stable API.

Backward compatibility ensures that the API continues to work the same way with consumers’ applications, regardless of the changes that occur. You can easily ensure backward compatibility by introducing unit tests to verify that functionality remains across different versions of your API. Specifically, you want to verify that API endpoints return the same response schemas and accept the same request schemas. Ideally, you want to implement continuous integration that runs for each change against your API. This practice automates the validation of backward compatibility. If a unit test fails, your continuous integration pipeline can warn you to avoid releasing the update.

By implementing backward compatibility, an API producer can offer a more stable API and reduce communication about API changes to consumers. Moreover, this practice reduces the number of documentation changes and versions needed to reflect API changes.

2. Document All API Versions and Publish Changelogs

Be sure to support all API versions with documentation. Some companies only provide documentation for the latest API version, meaning that clients consuming older API versions cannot find relevant information.

A changelog that describes all changes in each new API release is one of the most important reference documents for API consumers. It allows them to verify that changes won’t negatively affect their application, so they can decide whether they want to update.

The ability to quickly update API consumers about new releases is vital, so it’s a good idea to provide a variety of ways to subscribe to changelog updates, like via an RSS feed and through email updates. This ensures that API consumers can change their applications to reflect API changes.

3. Avoid Changing Endpoints or Response Formats

To minimize the risk of breaking features, add new endpoints instead of changing existing ones. Additionally, you should add new properties to the response format instead of changing existing properties.

Assume, for example, that you have an API endpoint that returns information about individual people. Currently, each person can have just one phone number. However, perhaps due to changing business requirements or customer feedback, you now want to support multiple phone numbers for each person. Instead of changing the phone field to an array, you add a new property: phones. This ensures backward compatibility and allows you to change the functionality of your API.

Likewise, you don’t want to remove support for old API endpoints. Instead, add new API endpoints that support the updated business requirements.

By following this strategy, you can ensure backward compatibility for API endpoints and avoid breaking client applications.

4. Opt for Versioning Through the URI Path

There are many API versioning strategies. One of the best ways is to include the API version in the URI path. Many large companies like Facebook, Twitter, and Airbnb have adopted this strategy.

This type of URI routing enables clients to a specific version of your API. It’s a straightforward way of telling an application which version it’s consuming. You can also host multiple versions of your API, allowing consumers to choose which version they want to use. Furthermore, this approach enables easy resource caching.

5. Publish an Up-to-Date Release Schedule

A release schedule lets you inform API consumers of upcoming changes and new API versions. When you decide to deprecate or remove support for an older version, your API consumers have ample time to refactor their applications. Install monitoring to measure how many applications are consuming each API version. You don’t want to pull support before your users have migrated to the new version. This is an important aspect of being a quality API provider.

In short, an up-to-date release schedule allows API consumers to anticipate upcoming API changes. Instead of having to take down their application for maintenance, they can continue operating with minimal downtime, mitigating any loss of business revenue. Furthermore, a release schedule allows API consumers to clearly communicate their future plans and prepare for upcoming API changes.

Conclusion

An API contract enables API providers to clearly communicate with consumers about their interface. To strengthen communication, publish changelogs and offer documentation for each API version. Make sure to provide simple ways for API consumers to subscribe to these updates to ensure all your consumers can easily receive these updates. By versioning your API via the URI path, you offer an explicit way of API versioning, which makes it easy for API consumers to switch between API versions.

API versioning is an essential aspect of offering a reliable, stable, high-quality API. While breaking changes can and sometimes must be introduced, it’s best to limit them and enforce backward compatibility where possible. When companies have to deal with many breaking changes, they’re likely to look for more stable alternatives with lower maintenance costs.