API Versioning Made Simple: Strategies, Best Practices, and Real Examples
Learn API versioning strategies (URI, query, header, media type) with real examples. Keep APIs backward compatible and deprecate safely.
API versioning helps teams evolve their APIs without breaking existing clients. This blog covers common versioning strategies—URI, query, header, and media type—along with backward compatibility practices and safe deprecation methods, supported by real-world examples.
When you update an API to add features or fix issues, you risk breaking the applications that depend on it.
API versioning is the practice of managing changes in an API so that existing clients continue to work while new features are introduced. It ensures backward compatibility, meaning older clients can still use the API without errors, even as the API evolves.
In this blog, we’ll explore why versioning matters, common versioning strategies, how to maintain backward compatibility, and how to deprecate old API versions gracefully.
Why Versioning (and Backward Compatibility) Matters
APIs (Application Programming Interfaces) are the contracts that let different software systems communicate.
When an API changes unexpectedly, it can break those integrations and disrupt users’ experience or business operations.
Backward compatibility means that new versions of an API do not break existing clients.
Achieving this often requires providing multiple versions of the API or carefully designing changes so they are non-breaking.
By using versioning, you can improve an API without forcing clients to immediately rewrite their integration code. This is especially true for public APIs, but even internal APIs benefit from avoiding sudden breaking changes.
Offering stable, versioned APIs builds trust: clients know that their integration will continue to work over time or that they will be given plenty of notice to migrate to a newer version.
Common API Versioning Strategies
There are multiple strategies to version an API, each with pros and cons.
The right choice depends on your API’s audience, how it’s used, and how you prefer to manage changes.
Here are some common versioning methods:
URI Path Versioning
Probably the simplest approach: include the version number in the URL path.
For example, you might have endpoints like /api/v1/users and /api/v2/users for version 1 and 2 of a users resource.
Pros: It’s very clear and easy for clients to understand which version they are calling.
Cons: It can clutter your URL space, and each major version might require duplicating a lot of code or maintaining separate codebases for each version.
Query Parameter Versioning
In this method, the client specifies the version in a query string.
For example: GET /api/users?version=2. This keeps the base URL the same and just passes the version as a parameter.
Pros: It’s easy to implement and test (you can hit different versions just by changing a URL parameter).
Cons: It can be harder for the server to route requests to the correct version.
Header Versioning
The version is supplied via an HTTP header rather than the URL. This can be a custom header (e.g. X-API-Version: 2) or using the Accept header with a versioned media type.
For example, a request might include Accept: application/vnd.myapi.v2+json to indicate version 2 of the response format.
Pros: This keeps version details out of the URL, making endpoints look cleaner and allowing version negotiation at the HTTP header level.
Cons: It’s less obvious to clients and requires extra steps for testing (you must set custom headers, unlike path or query versions).
Each strategy above aims to let clients specify which version of the API they want.
Importantly, you should start versioning early if you anticipate growth – it’s easier than retrofitting versioning after an API is already in use.
Also, be consistent: if you choose one versioning method, use it uniformly across your API products to avoid confusion.
Semantic version numbers (Major.Minor.Patch) are commonly used to signal the scope of changes in an API.
For example, a jump from version 1.x to 2.0 indicates breaking changes, while moving from 2.0 to 2.1 might add features without breaking existing clients.
Many APIs use a simple integer (v1, v2) in URLs for major versions, and track minor/patch changes separately in documentation or headers.
Using semantic versioning helps communicate the nature of changes: increment the major version for incompatible API updates, the minor for backward-compatible improvements, and the patch for bug fixes.
Check out 20 API Interview questions.
Best Practices for Backward Compatibility
The golden rule of evolving an API is don’t break existing clients.
Here are some best practices to maintain backward compatibility as you introduce changes:
Prefer Additive Changes: Whenever possible, add new endpoints or fields instead of changing or removing existing ones. For example, if your v1 API returns a field phone (a single value) and you need to support multiple phone numbers, resist the urge to change phone into an array in place. Instead, add a new field phones (an array) in v2, while still returning the original phone field for v1 clients. This way, old clients remain unaffected and new clients can utilize the expanded functionality.
Avoid Immediate Removal or Renaming: If you need to retire a field or endpoint, deprecate it but keep it functional until you officially drop support in a future version. Mark fields or endpoints as “deprecated” in your documentation (or even return a warning header) but continue to serve them until the next major version. This gives clients time to migrate.
Rigorous Multi-Version Testing: Invest in automated tests that verify older versions still behave as expected after changes. This includes contract tests to ensure the response schema and data types haven’t changed unexpectedly for legacy versions. Run a full test suite for each API version in your CI/CD pipeline. Catching these issues early prevents accidentally breaking compatibility in production.
Deprecating and Retiring API Versions
Even with great care for backward compatibility, eventually old versions need to be retired to reduce maintenance overhead.
Deprecation is the process of signaling that a feature or version will be phased out, and retirement (or sunsetting) is when it’s finally removed.
To evolve your API safely, you need a clear deprecation strategy:
Advance Notice: Always announce deprecation well ahead of time. A common practice is to give at least 6 to 12 months notice before an old API version is shut off. Also, make it clear to clients that they are using a deprecated version – for example, send a header in responses (such as a Deprecation: true flag or a sunset date) to signal this.
Provide a Migration Path: Offer guidance to help developers upgrade to the new version. Publish migration guides or release notes highlighting what changed (for example, if v2 renames or replaces certain fields from v1, point that out clearly). This way, your users know exactly what code changes are needed to move to the newer API.
Support Overlap: Run the old and new versions in parallel. This grace period allows clients to test and migrate at their own pace. Encourage users to switch to v2, but don't shut off v1 immediately. Monitor usage of v1 to decide when it's safe to fully retire it.
Sunset and Remove: After the deprecation window, fully shut down the old version. Disable its endpoints and archive its documentation. Ideally, calls to a retired API version should return a clear error (e.g. HTTP 410 Gone) indicating it’s no longer supported. If your deprecation process was successful, very few users will still be on the old version at this point.
Conclusion
Managing API changes through versioning allows you to add new features without breaking existing integrations.
A consistent versioning strategy ensures you maintain the trust of your API consumers.
By evolving your APIs safely, you can continue to innovate without leaving any users behind.
For more on API basics, read our guide on what an API is and the four types of APIs. If you’re preparing for interviews, API versioning is a common topic – see Mastering the API Interview for more.
FAQs
Q1: What is the best way to version a REST API?
The most common approach is URI versioning (e.g., /v1/resource). It’s easy to understand and widely supported. However, header versioning and content negotiation are also popular when you want cleaner URLs or finer control. The “best” way depends on your API’s audience and how strictly you need to manage backward compatibility.
Q2: How do you maintain backward compatibility in APIs?
To keep APIs backward compatible, avoid removing or changing existing fields. Instead, add new endpoints or properties, mark old ones as deprecated, and support both versions in parallel until clients migrate. Automated testing for older versions ensures you don’t accidentally break them.
Q3: What does it mean to deprecate an API?
Deprecating an API means signaling that a version or feature will be phased out. The API still works, but developers are encouraged to migrate to a newer version. Deprecation should always include clear documentation, warnings (e.g., headers), and an advance timeline before the API is finally retired.