API Versioning: The Complete Guide for Developers and Product Managers
If you want to cultivate a thriving ecosystem of integrations and partnerships around your application, you need to build trust with the developers who use your API. And the foundation of that trust is a stable, predictable API.
But here‘s the challenge: like any software, APIs need to evolve and improve over time. How can you make necessary updates to your API without pulling the rug out from under your integration partners? The answer is API versioning.
In this in-depth guide, we‘ll cover everything you need to know about API versioning – what it is, why it matters, when to use it, and API versioning best practices. We‘ll also compare four common methods for specifying API versions in client requests, complete with code samples.
By the end of this post, you‘ll have a solid foundation to build your own API versioning strategy to keep your integrations humming along smoothly as your API evolves. Let‘s dive in!
What is API Versioning?
API versioning is the practice of managing changes to your API‘s interface in a way that doesn‘t disrupt existing integrations. With proper API versioning, you can make updates and improvements to your API while allowing API consumers to upgrade to the new version when they‘re ready, not on your timeline.
Think of API versioning like managing software updates. When Google releases a new version of Chrome, they don‘t force the update on all users at once. Users can choose to download the latest version when it‘s convenient for them, or keep using an older version if they prefer. Meanwhile, Google continues supporting older versions for a period of time before eventually sunsetting them.
API versioning follows a similar principle. When you make a significant change to your API, you release it as a new version while still supporting the previous version. This gives developers flexibility to upgrade their integrations on their own schedule.
Why API Versioning Matters
Imagine you‘ve built an integration with a business-critical API. Your app relies on the API to function and generate revenue. Now imagine waking up one day to find the API made a breaking change without warning, and now your integration is down. You‘re losing money every minute until you can drop everything to fix it.
This is the nightmare scenario that proper API versioning prevents. Breaking changes to an API can have costly ripple effects across every integration and dependent service. But by releasing breaking changes in a new API version, and clearly communicating the change well in advance, you can avoid nasty surprises and frustrated developers.
Beyond preventing headaches, API versioning is also critical for growing an integration ecosystem. Third-party developers are much more likely to build on an API with a history of stability and a clear versioning policy. No one wants to build an integration only to have the maintenance costs spike every time the API makes an unannounced change.
As Ronnie Mitra, Director of API Design at Salesforce, puts it: "The most important promise an API provider can make is to grow your API without requiring updates to your developer‘s code." API versioning gives developers confidence that their integrations will remain stable, even as the underlying API evolves.
When to Version Your API (and When Not To)
As a general rule, you should cut a new API version whenever you make a breaking change to your API‘s interface. A breaking change means modifying the API in a way that would cause existing integrations to break without updating their code.
Some examples of breaking API changes that warrant a new version:
- Removing or renaming an API endpoint
- Changing the data type or structure of a request/response payload
- Adding a new required field to an existing request payload
- Changing authentication methods
On the flip side, you typically don‘t need a new version for backwards-compatible changes, like:
- Adding an entirely new API endpoint
- Adding new optional request parameters
- Adding new fields to an existing response payload
These non-breaking changes can be made to your existing API version without forcing updates to existing integrations. Avoid cutting a new version unless truly necessary, since each additional version means more code to maintain over time.
Sometimes you can accomplish the same goal through a non-breaking change instead of a breaking change. For example, instead of renaming or removing a response field, consider deprecating the old field and adding a new field alongside it. You can support both for a time while encouraging developers to migrate to the new field.
The key is to treat your API interface as a contract with your users. Avoid breaking that contract unless you have no other option. And when you do, cut a new version and give developers ample runway to adapt before shutting off the old version.
API Versioning Best Practices
We‘ve covered when and why to version your API. Now let‘s discuss some API versioning best practices to minimize friction for your integration partners.
1. Maintain Backwards Compatibility
When you release a new API version, keep the previous version running in parallel for a time so developers don‘t need to implement the new version immediately. This allows developers to upgrade their integrations on their own timelines.
How long should you maintain the old version? That depends on your API‘s user base and use case, but most APIs maintain at least the latest two versions at any given time. Stripe, for example, supports old API versions for a full year after the release of a new version.
Give developers sufficient notice before deprecating an old API version, and help them understand what will break if they don‘t upgrade by the cutoff date. Most APIs provide at least 6 months notice before sunsetting an old version.
2. Use Semantic Versioning
Semantic versioning is a standard for assigning version numbers to software in a way that conveys the type of change. Under semantic versioning, a version number takes the form MAJOR.MINOR.PATCH:
- MAJOR version increments represent breaking changes to the public API interface
- MINOR version increments represent backwards-compatible feature additions
- PATCH version increments represent backwards-compatible bug fixes
Most modern APIs use semantic versioning to clearly communicate the magnitude of changes in each new version. If you increment the MAJOR version, developers know to expect breaking changes that will require updates to their code. If you increment a MINOR or PATCH version, they know their existing code will continue working.
For example, an API might release the following sequence of versions:
- v1.0.0 – Initial stable release
- v1.0.1 – Bug fix in the v1.0 release
- v1.1.0 – New feature added in a backwards-compatible way
- v1.1.1 – Bug fix in the v1.1 release
- v2.0.0 – Breaking changes that require integration updates
Adopting semantic versioning makes your API predictable and transparent for your consumers.
3. Communicate Early and Often
Never make your API consumers read the tea leaves to understand what‘s changing in your API and how it affects them. Over-communicate about all changes to your API, whether breaking or non-breaking.
When you release a new API version, shout it from the rooftops! Write clear release notes detailing what changed, and provide instructions and code samples showing how developers should update their integrations. Most API-first companies have a dedicated changelog for their API.
You‘ll also want to communicate the timeline for when you plan to deprecate the old API version. Send announcements via your developer newsletter, social channels, and directly to partners. Consider building a migration guide to help developers upgrade by the cutoff date.
4 Ways to Version Your API
There are a few different approaches for specifying which version of your API a client wants to call. Let‘s look at four of the most popular API versioning methods, along with their pros and cons.
1. URI Path Versioning
With URI versioning, the API version is specified directly in the endpoint paths:
https://api.example.com/v1/users
https://api.example.com/v2/usersURI versioning is simple, intuitive, and SEO-friendly since each version has its own URLs. However, it also means you need to fully replicate every API endpoint across versions, which can lead to redundant code.
2. Query Parameter Versioning
Query parameter versioning specifies the API version in the query string of the URL:
https://api.example.com/users?version=1
https://api.example.com/users?version=2This approach avoids the need to version every individual URI path. It‘s also easy for API consumers to override the version on a per-request basis.
3. Custom Headers
You can specify the API version in a custom HTTP request header, typically named something like X-API-Version:
GET /users HTTP/1.1
Host: api.example.com
X-API-Version: 1Custom header versioning keeps your URIs clean and tidy. But it‘s a bit more cumbersome for API consumers compared to specifying the version directly in the URL.
4. Content Negotiation
Content negotiation uses the built-in HTTP Accept header to specify the desired API version as part of the requested media type:
GET /users HTTP/1.1
Host: api.example.com
Accept: application/json; version=1This approach also keeps your base URIs clean while avoiding the need for custom headers. The downside is that tying version to media type doesn‘t allow retrieving different versions of the same resource representation.
So which API versioning method should you choose? There‘s no one-size-fits-all answer. But in general, URI path versioning and query parameter versioning tend to be the most straightforward for API consumers, while custom header and content negotiation offer more flexibility at the cost of a steeper learning curve.
Whichever method you choose, the most important thing is to be consistent across your API. Don‘t mix and match versioning schemes, or you‘ll end up confusing your consumers.
Building Trust Through API Versioning
We‘ve covered a lot of ground in this guide to API versioning, but it all boils down to one key idea: API versioning is about building trust.
When third-party developers choose to integrate with your API, they‘re entering into a partnership with you. They‘re counting on your API to remain stable and predictable, even as their business grows and scales. Nothing erodes that trust faster than seeing their integration go down because of an unannounced breaking change to your API.
By adopting a clear API versioning strategy and sticking to it, you demonstrate to developers that you‘re a reliable partner. You show that you respect their investment in your platform, and that you‘ll work with them to keep their integrations running smoothly.
API versioning takes extra planning, communication, and maintenance compared to pushing out API changes ad hoc. But that extra effort pays huge dividends in developer experience and trust. And at the end of the day, that trust is the secret ingredient to growing a vibrant ecosystem around your API.
