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OpenApi Custom Extensions

· 3 min read

OpenAPI is a specification for designing and describing RESTful APIs. The OpenAPI extension, also known as the OpenAPI specification extension, is a way to add additional information to an API definition. In OpenAPI specifications, extensions allow adding vendor-specific or custom fields to a specification document. They are defined as a field in the specification with the key starting with "x-", for example, "x-vendor-field". The contents and meaning of these extensions are specific to the vendor or tool using them and are not part of the OpenAPI specification.

OpenAPI extensions can help designers in several ways:

  • Adding custom fields: Extensions allow designers to add custom fields to the OpenAPI specification, which can provide additional information about the API and enhance the design.

  • Enhancing tool support: By using extensions, designers can add functionality specific to their tools or workflows and improve the tool support for their API design.

  • Improving collaboration: Extensions can be used to share additional information between different teams and stakeholders involved in the API design process, enhancing collaboration and communication.

  • Supporting vendor-specific features: Extensions can support vendor-specific features, such as specific security protocols or data formats. The core OpenAPI specification may not support that.

  • Streamlining development: By using extensions, designers can simplify the development process and ensure that all necessary information is included in the specification, reducing the risk of miscommunication or misunderstandings.


The "x-badges" extension in OpenAPI specifications allows designers to display badges, or small graphical elements, in the API documentation. These badges can be used to provide additional information about the API or to highlight specific features.

Here are some of the ways that "x-badges" can help with OpenAPI specifications:

  • Showing API status: Badges can be used to indicate the status of an API, such as "beta" or "deprecated." This information helps developers understand the current state of the API and whether it is appropriate to use.

  • Highlighting important information: Badges can highlight important information about the API, such as the version number, release date, or supported platforms. This information can be displayed prominently in the API documentation, making it easier for developers to find.

  • Providing visual cues: Badges can give visual cues that draw attention to specific information in the API documentation. This makes it easier for developers to find the information they need quickly.

Overall, the "x-badges" extension in OpenAPI specifications provides a simple and effective way to display additional information about the API. By using badges, designers can improve the usability and clarity of their API documentation.

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Providing sample code: The "x-code-sample" extension can be used to include sample code snippets for different programming languages. This can help developers understand how to use the API and make it easier for them to get started.


Defining authentication information: The "x-client-id" and "x-client-secret" extensions can be used to define the client ID and secret required for authentication with the API. This can help ensure that developers have the information they need to properly use the API.


Enforcing security measures: The "x-pkce-only" extension can be used to enforce the use of Proof Key for Code Exchange (PKCE) in OAuth 2.0. This is a security measure that helps prevent unauthorized access to an API.


In summary, the OpenAPI extension allows designers to provide additional information and constraints to the API definition, making it easier for developers to understand and use the API. By using extensions, designers can improve the usability and security of their APIs.