If you need easy-to-understand APIs and seamlessly interoperable applications, the OpenAPI Specification (OAS) is the answer. The OAS is a powerful tool in API design and development, providing a solid foundation for consistent, easy-to-understand APIs. Below, we show you some of OpenAPI’s key benefits, core concepts, and best practices. Whether you produce or consume APIs, understanding the OAS is critical to creating interoperable applications.
The OpenAPI Specification: A brief overview
The OAS is an open standard for defining and structuring REST APIs. It allows you to describe APIs in language-agnostic and vendor-neutral terms, separating them from specific programming languages.
OpenAPI documents can be read by machines and humans, making it easy for consumers to understand an API’s purpose and functionality.
Why should developers use OpenAPI?
OpenAPI allows developers to streamline and improve API design and development processes. Some of the key benefits of using OpenAPI include:
- Better API documentation: Developers can use OpenAPI to provide clear and comprehensive documentation for their APIs. They can use OpenAPI documents to generate interactive API documentation, helping consumers quickly understand how an API works.
- Automating processes: OpenAPI has a large development community, with numerous tools available for automating the API design and development process — from generating mock servers and client libraries to automatic API response validation and linting.
- Improved collaboration: OpenAPI allows parties to come together early in the design process, long before writing any code. The specification serves as a contract that teams can work from, creating an understanding as to what the API should do. This contract helps reduce misunderstandings and integration problems.
- Better interoperability: OpenAPI provides a standard language for describing APIs, facilitating improved interoperability between various services, applications, and systems. It helps simplify integrations with tools and frameworks that support the specification.
- Ability to articulate workflows: OpenAPI’s separate but complementary specification, Arazzo, lets you articulate sequences of calls and the dependencies between them for a specific outcome or set of outcomes. It allows you to explain functional use cases and workflows for an API or group of APIs.
OpenAPI core concepts
Core concepts you should know about the OpenAPI specification include:
- Paths: Paths represent the API’s endpoints and HTTP operations. Operations are the methods available for each endpoint, e.g., GET, POST, PUT, DELETE. Each path has a specific Uniform Resource Identifier (URI) and can have multiple operations.
- Parameters: Parameters describe the input or values for an operation. They include path, header, query, cookie, and request body. You typically use parameters to identify a resource and a request body to provide content for that identified resource.
- Schemas: An OpenAPI schema defines the data’s underlying structure, usually in JSON format. It defines the API elements, such as endpoints, headers, request and response formats, and authentication methods.
- Security schemes: OpenAPI lets you define security schemes across your APIs, meaning you can set supported authentication and authorization methods. For example, OpenAPI v3.1 supports security schemes, such as OAuth2, mutual TLS (mTLS), and OpenID Connect Discovery.
- Components: Components help reduce API redundancies by allowing you to reuse definitions for various parts of the API, such as headers, responses, schemas, parameters, and security schemes. You can reference components throughout the API definition.
With a good grasp of these core concepts, API producers and consumers can maximize OpenAPI by following the best practices below.
OpenAPI best practices
Using OAS effectively helps you produce consistent, high-quality APIs. Here are some best practices to follow:
- Use clear, concise, and consistent naming conventions:
- Use clear and concise names for elements throughout your OpenAPI documents.
- When naming paths, stick with one convention like hyphens, snake case, or camel case.
- Keep titles, names, and summaries under 50 characters to avoid issues with code generation tools.
- Define your security schemes: Make sure you’ve clearly defined your security schemes with standard authentication and authorization methods like OAuth2 and mTLS. Also, document how clients should authenticate API endpoints. Once you’ve defined your security schemes, you can apply them to the entire API or individual operations.
- Reuse components: Reusing components like parameters, responses, and schemas helps prevent OpenAPI files from becoming large and unmanageable. OpenAPI (v3.0+) includes a Components Object, which holds sets of reusable objects, such as schemas, responses, parameters, examples, and security schemes.
- Always validate: Use automated tools to ensure that various aspects of your API adhere to the OAS. For example, you could use a linter to see if your JSON schemas meet the current version of OpenAPI. An automated tool can also help you ensure that your API complies with an OpenAPI-based style guide.
- Provide examples: OpenAPI has dedicated fields where you can add examples for different API elements. Adding an example for as many elements as possible helps clarify what your API does. Tools can then use these examples for purposes like creating mock APIs. You could include examples for parameters, request and response bodies, objects, and individual properties.
- Include contact information: Although optional, you should include your contact information in OpenAPI’s contact field. This field contains three properties — name, URL, and email — giving API consumers a way to reach you if they need support.
These are only some of the best practices for creating APIs using OpenAPI. You can discover more essentials for producing API descriptions using OAS.
The OpenAPI Specification: A vital tool in producing quality APIs
OpenAPI provides benefits for both API producers and consumers. You can use it to ensure consistency across your APIs and to automate processes throughout the design and development stages.
When API producers maximize OAS, consumers get high-quality APIs that are easier to understand and use. Best of all, many tools already support the OpenAPI Specification — Tyk 5.3+ includes native support for OAS!
