OpenAPI Specification vs Pact: What are the differences?

The OpenAPI Specification (OAS) and Pact are two widely used tools for API documentation and testing. While they serve similar purposes, there are several key differences between them.

1. Flexibility of Use: OAS is a more flexible tool as it allows for documenting APIs in a variety of formats, such as YAML or JSON. On the other hand, Pact is primarily designed for testing interactions between consumers and providers of APIs.

2. Focus on Contract Testing: Pact is specifically designed for contract testing, ensuring that the consumer and provider of an API can communicate effectively. In contrast, OAS is a more general tool that covers various aspects of API documentation, including request and response structure, authorization, and more.

3. Consumer-Driven vs Provider-Driven: Pact follows the consumer-driven contract testing approach, where the consumer defines the expectations and the provider ensures they are met. OAS, on the other hand, provides a more provider-centric approach, where the provider defines the API specification, and the consumer relies on it for documentation and testing.

4. Level of Detail: OAS is known for providing comprehensive documentation and specification details, including endpoints, parameters, request and response payloads, and more. Pact, however, focuses more on the specific interactions between the consumer and provider, ensuring that they are correctly implemented and without breaking changes.

5. Tooling Ecosystem: OAS has a larger tooling ecosystem with a wide range of plugins, editors, and validators available. This makes it easier to work with OAS in different environments. Pact, on the other hand, has a more focused tooling ecosystem specifically built around contract testing, providing support for various programming languages.

6. Collaboration and Versioning: OAS supports collaboration among multiple contributors using source control systems, allowing for easier versioning and tracking of changes. Pact, on the other hand, focuses more on versioning and maintaining contract tests across different versions of the API, ensuring compatibility and avoiding breaking changes.

In Summary, OAS is a more general and flexible tool for API documentation, while Pact is specifically designed for contract testing and ensuring the compatibility between consumers and providers of APIs.