OpenAPI vs REST: What are the differences?

Introduction: OpenAPI and REST are two technologies commonly used in web development. While they share some similarities, there are key differences between the two that set them apart. In this article, we will highlight six major differences between OpenAPI and REST.

1. Data Schema Definition: One significant difference between OpenAPI and REST is the approach used for defining data schemas. OpenAPI utilizes a separate file, typically in JSON or YAML format, to define the structure and properties of APIs. This allows for a more standardized and centralized way of describing data models. On the other hand, REST relies on custom data structures embedded within the API implementation itself, making it less formalized and more flexible.

2. Request and Response Format: OpenAPI defines a standardized request and response format using either JSON or XML schemas. This ensures consistency in how the data is structured and exchanged between clients and servers. In contrast, REST does not enforce a specific format for requests and responses, leaving it up to the developer to determine the structure and format based on their specific needs.

3. API Documentation: One of the main benefits of OpenAPI is its built-in support for generating API documentation. By leveraging the defined data schemas and annotations, OpenAPI tools can automatically generate comprehensive documentation, making it easier for developers to understand and consume the API. REST, on the other hand, often requires manual documentation efforts, which can be time-consuming and error-prone.

4. API Versioning: OpenAPI provides a standardized way to handle API versioning. APIs can be versioned by adding a version identifier to the URL or request header, allowing clients to use the specific version they require. REST does not offer a built-in mechanism for versioning, leaving it up to developers to implement their own versioning strategy, which can vary across different APIs.

5. API Discovery: OpenAPI supports automatic API discovery through its standardized schema definition. This means that clients can easily discover available APIs, their endpoints, and supported operations without manual intervention. REST does not have a standardized mechanism for API discovery, requiring clients to rely on external documentation or trial-and-error to find the required endpoints and operations.

6. Tooling and Ecosystem: OpenAPI has a vibrant tooling and ecosystem built around it. There are various tools and frameworks that support OpenAPI, allowing for seamless integration with other technologies and providing additional features like API mocking, testing, and client generation. REST, being a more general architectural style, does not have a dedicated ecosystem, although there are many libraries and frameworks available that facilitate building RESTful APIs.

In Summary, OpenAPI and REST differ in their approach to data schema definition, request/response format, API documentation, versioning, API discovery, and the tooling/ecosystem available around them.