# Open API specification

To describe the REST APIs, BoldSign uses the Open API specification. This {% customlink href="https://api.boldsign.com/swagger/v1/swagger.json" text="Open API specification file" /%} served as the foundation for the creation of our C# client library. Additionally, you can use it to create your own client library for any platform or coding language. You might need to re-import our Open API definition file from time to time because we occasionally update it.

Read more about {% customlink href="/api-overview/client-libraries/" text="client libraries" /%} for ready-to-use SDKs.