Google Cloud APIs are programmatic interfaces to Google Cloud Platform services, which allow developers to easily add the power of everything from computing to networking to storage to machine-learning-based data analysis to their applications. These APIs are exposed as network API services to customers and provide both JSON HTTP and gRPC interfaces to clients over public internet and Virtual Private Cloud (VPC) networks.

The purpose of these APIs is to allow developers to automate their workflows by using their favorite language, with REST calls or client libraries in popular programming languages. They provide access to computing resources and data, which greatly increases a developers efficiency and allows them to use APIs built with the developer in mind.

Google offers APIs that can be applied to many different fields and sectors, including web development, machine learning, data science, and system administration workflows. The Cloud APIs can be accessed from server applications using current libraries, and access to the same services is also available via command.

The Cloud APIs are shared among millions of developers and users, and to ensure fair usage and minimize abuse risks, all Cloud APIs are enforcing rate limits and resource quotas on usage, commonly known as quotas. There are three types of authentication/authorization services that Google APIs use: API Keys, Service accounts, and OAuth.

In summary, the purpose of Google Cloud APIs is to provide developers with programmatic interfaces to Google Cloud Platform services, allowing them to automate their workflows and access computing resources and data in an efficient manner.