Creating an API definition

You can create API definitions by using the API Designer or the command line interface in IBM® API Connect.

Before you begin

An API is a set of functions that provide some business or technical capability and can be called by applications by using a defined protocol. Applications are typically mobile or web applications, and they use the HTTP protocol. An API definition is composed of paths, and can be one of the following types:

REST API definition

A REST API is a defined set of interactions that uses the HTTP protocol, typically by using JSON or XML as the data format that is exchanged. For example, a data request might use an HTTP GET method, and a data record might use an HTTP POST method. The choice of data format depends on the type of application that is calling the API. JSON is commonly used for web pages or mobile applications that present a user interface (by using JavaScript or HTML), whereas XML is often used for machine-to-machine scenarios.

You can create REST APIs by using LoopBack® functions to create models and data sources. These are then used by your REST API definition and exposed to your users.

Alternatively, you can expose and secure your existing APIs by using a Proxy or Invoke policy.

In either case, you can configure your API definition either by using the API Designer, or by writing an OpenAPI definition file and publishing it using either API Designer or the command line interface.


You can create SOAP API definitions that are based on an existing Web Services Description Language (WSDL) file. You can use this facility to benefit from the capabilities that are provided by API Connect, which include analytics and mapping between variables. You can also expose the API by using the Developer Portal for any existing SOAP services in your organization, including any SOAP services that are part of a service-oriented architecture (SOA) or Enterprise Service Bus (ESB) infrastructure.

You can create SOAP API definitions through either the command line interface, or through API Designer.

About this task

You can create definitions for REST APIs or SOAP APIs.

  • In the API Designer, you can add a REST API definition either by composing the API definition, and its operations, from scratch, or by importing an OpenAPI definition file. You can also use the tooling to quickly create a proxy API that calls an existing endpoint.
  • If you have an existing SOAP service that you want to expose more widely, you can add a SOAP API to IBM® API Connect. You can use the Developer Portal to publicize the SOAP service to the developers. If a developer wants to use the SOAP API, you can use API Connect to manage their sign-up and access to the service, and track the usage of that API.


  1. Quickly create an API definition by using one of the following wizards:
  2. After you create your API definition, you can define it in more detail by following the instructions in Editing an OpenAPI 2.0 API definition.