Use the Discovery API

This document is intended for developers who want to write client libraries, IDE plugins, and other tools for interacting with Google APIs. The Google APIs Discovery Service allows you to do all of the above by exposing machine readable metadata about other Google APIs through a simple API. This guide provides an overview of each section of the Discovery document, as well as helpful tips on how to use the document.

All calls to the API are unauthenticated, JSON-based, REST requests that use SSL—in other words, URLs begin with https.

Discovery document format

This section gives an overview of the Discovery document.

All the examples below use the Discovery document from the Service Usage API. You can load the Discovery document for the Service Usage API by executing this GET request:

GET https://serviceusage.googleapis.com/$discovery/rest?version=v1

The format of a Discovery document includes information that falls into six main categories:

Basic description of the API.
Authentication information for the API.
Resource and schema details describing the API's data.
Details about the API's methods.
Information about any custom features supported by the API.
Inline documentation that describes key elements of the API.

Each of these Discovery document sections is described below.

Basic API Description

The Discovery document contains a set of API-specific properties. These properties don't necessarily appear in this order, or in the same section of the discovery doc:

"id": "serviceusage:v1",
"canonicalName": "Service Usage",
"revision": "20240331",
"servicePath": "",
"baseUrl": "https://serviceusage.googleapis.com/",
"kind": "discovery#restDescription",
"description": "Enables services that service consumers want to use on Google Cloud Platform, lists the available or enabled services, or disables services that service consumers no longer use.",
"ownerDomain": "google.com",
"version_module": true,
"version": "v1",
"fullyEncodeReservedExpansion": true,
"name": "serviceusage",
"title": "Service Usage API",
"discoveryVersion": "v1",
"rootUrl": "https://serviceusage.googleapis.com/",
"protocol": "rest"

These API-level properties include details about a particular version of an API, including the name, version, title and description. The protocol always has a fixed value of rest, as the APIs Discovery Service only supports RESTful methods of accessing the APIs.

The servicePath field indicates the path prefix for this particular API version.

Authentication

The auth section contains details about the OAuth 2.0 auth scopes for the API. To learn more about how to use scopes with OAuth 2.0, visit Using OAuth 2.0 to Access Google APIs.

The auth section contains a nested oauth2 and scopes section. The scopes section is a key/value mapping from the scope value to more details about the scope:

"auth": {
  "oauth2": {
    "scopes": {
      "https://www.googleapis.com/auth/cloud-platform": {
        "description": "See, edit, configure, and delete your Google Cloud data and see the email address for your Google Account."
      },
      "https://www.googleapis.com/auth/cloud-platform.read-only": {
        "description": "View your data across Google Cloud services and see the email address of your Google Account"
      },
      "https://www.googleapis.com/auth/service.management": {
        "description": "Manage your Google API service configuration"
      }
    }
  }
}

The auth section only defines the scopes for a particular API. To learn how these scopes are associated with an API method, consult the Methods section below.

Resources and schemas

An API's operations act on data objects called resources. The Discovery document is built around the concept of resources. Each Discovery document has a top-level resources section that groups all the resources associated with the API. For example, the Service Usage API has a services resource and an operations resource under top-level resources:

"resources": {
  "services": {
    // Methods associated with the services resource
  }
  "operations": {
    // Methods associated with the operations resource
  }
}

Inside each resource section are the methods associated with that resource. For example, the Service Usage API has six methods associated with the services resource: get, enable, disable, batchGet, batchEnable, and list.

Schemas tell you what the resources in an API look like. Each Discovery document has a top-level schemas section, which contains a name/value pair of schema ID to object. Schema IDs are unique per API, and are used to uniquely identify the schema in the methods section of the Discovery document. For example, here are a few of the schemas in the Service Usage API Discovery document:

"schemas": {
  "Method": {
    // JSON schema of the Method resource
  },
  "Authentication": {
    // JSON schema of the Authentication resource
  },
  "RubySettings": {
    // JSON schema of the RubySettings resource
  },
  "EnableServiceResponse": {
   // JSON schema of the EnableServiceResponse resource
  }
}

APIs Discovery Service uses JSON Schema draft-03 for its schema representations. The following is a snippet of the JSON Schema for the EnableServiceResponse resource, along with the GoogleApiServiceusagev1Service that it references. Alongside these schemas is a portion of an actual response for a request to enable the Pub/Sub API (pubsub.googleapis.com).

EnableServiceResponse Resource JSON Schema: Actual response for enabling a service:

"EnableServiceResponse": {
  "id": "EnableServiceResponse",
  "description": "Response message for the `EnableService` method. This response message is assigned to the `response` field of the returned Operation when that operation is done.",
  "properties": {
    "service": {
      "description": "The new state of the service after enabling.",
      "$ref": "GoogleApiServiceusageV1Service"
    }
  },
  "type": "object"
},
"GoogleApiServiceusageV1Service": {
  "description": "A service that is available for use by the consumer.",
  "properties": {
    "config": {
      "$ref": "GoogleApiServiceusageV1ServiceConfig",
      "description": "The service configuration of the available service. Some fields may be filtered out of the configuration in responses to the `ListServices` method. These fields are present only in responses to the `GetService` method."
    },
    "name": {
      "type": "string",
      "description": "The resource name of the consumer and service. A valid name would be: - projects/123/services/serviceusage.googleapis.com"
    },
    "state": {
      "enumDescriptions": [
        "The default value, which indicates that the enabled state of the service is unspecified or not meaningful. Currently, all consumers other than projects (such as folders and organizations) are always in this state.",
        "The service cannot be used by this consumer. It has either been explicitly disabled, or has never been enabled.",
        "The service has been explicitly enabled for use by this consumer."
      ],
      "description": "Whether or not the service has been enabled for use by the consumer.",
      "type": "string",
      "enum": [
        "STATE_UNSPECIFIED",
        "DISABLED",
        "ENABLED"
      ]
    },
    "parent": {
      "type": "string",
      "description": "The resource name of the consumer. A valid name would be: - projects/123"
    }
  },
  "id": "GoogleApiServiceusageV1Service",
  "type": "object"
}

"response": {
  "@type": "type.googleapis.com/google.api.serviceusage.v1.EnableServiceResponse",
  "service": {
    "name": "projects/232342569935/services/pubsub.googleapis.com",
    "config": {
      "name": "pubsub.googleapis.com",
      "title": "Cloud Pub/Sub API",
      "documentation": {
        "summary": "Provides reliable, many-to-many, asynchronous messaging between applications.\n"
      },
      "quota": {},
      "authentication": {},
      "usage": {
        "requirements": [
          "serviceusage.googleapis.com/tos/cloud"
        ]
      },
      "monitoring": {}
    },
    "state": "ENABLED",
    "parent": "projects/232342569935"
  }
}

The fields in bold show the mapping between the JSON Schema and the actual response.

As shown in this example, schemas can contain references to other schemas. If you are building a client library, this can help you effectively model the objects of an API in your data model classes. In the EnableServiceResponse example above, the service property is a reference to a schema with ID GoogleApiServiceusageV1Service, another schema in the Service Usage API Discovery document. You can substitute the GoogleApiServiceusageV1Service property in the EnableServiceResponse resource with the value of the GoogleApiServiceusageV1Service schema (note that the $ref syntax comes from the JSON Schema spec).

Methods may also reference schemas when indicating their request and response bodies. Refer to the Methods section for more details.

Methods

The core of the Discovery document is built around methods. Methods are the operations that can be performed on an API. You will find the methods section in various areas of the Discovery document, including at the top level (which we call API-level methods) or at the resources level.

"methods": {
  // API-level methods
}
"resources": {
  "resource1": {
    "methods": {
      // resource-level methods
    }
    "resources": {
      "nestedResource": {
        "methods": {
          // methods can even be found in nested-resources
        }
      }
    }
  }
}

While an API can have API-level methods, a resource must have a methods section.

Each methods section is a key-value map from method name to other details about that method. The example below documents three methods, get, enable and disable:

"methods": {
  "get": { //details about the "get" method },
  "enable": { //details about the "enable" method },
  "disable": { //details about the "disable" method }
}

Finally, each method's section details various properties about that method. Here is an example of the enable method:

"enable": {
  "path": "v1/{+name}:enable",
  "request": {
    "$ref": "EnableServiceRequest"
  },
  "parameterOrder": [
    "name"
  ],
  "id": "serviceusage.services.enable",
  "response": {
    "$ref": "Operation"
  },
  "description": "Enable a service so that it can be used with a project.",
  "httpMethod": "POST",
  "flatPath": "v1/{v1Id}/{v1Id1}/services/{servicesId}:enable",
  "scopes": [
    "https://www.googleapis.com/auth/cloud-platform",
    "https://www.googleapis.com/auth/service.management"
  ],
  "parameters": {
    "name": {
      "location": "path",
      "description": "Name of the consumer and service to enable the service on. The `EnableService` and `DisableService` methods currently only support projects. Enabling a service requires that the service is public or is shared with the user enabling the service. An example name would be: `projects/123/services/serviceusage.googleapis.com` where `123` is the project number.",
      "required": true,
      "type": "string",
      "pattern": "^[^/]+/[^/]+/services/[^/]+$"
    }
  }
},

This section contains general method details such as a unique ID to identify the method, the httpMethod to use, and the path of the method (for details on how to use the path property to calculate the full method url, see the Compose a request section). In addition to these general method properties, there are a few properties that connect the method with other sections in the Discovery document:

Scopes

The auth section defined earlier in this documentation contains information about all the scopes supported by a particular API. If a method supports one of these scopes, it will have a scopes array. There is one entry in this array for each scope supported by the method.

Note that choosing an auth scope to use in your application depends on various factors such as which methods are being called and what parameters are sent along with the method. Therefore, the decision of which scope to use is left to the developer. Discovery only documents which scopes are valid for a method.

Request and response

If the method has a request or response body, these are documented in the request or response sections, respectively. For example, for the enable method, the content of the request section indicates that the method's request is defined by a JSON schema with an ID of EnableServiceRequest. This schema can be found in the top-level schemas section.

Parameters

If a method has parameters that should be specified by the user, these parameters are documented in the method-level parameters section. This section contains a key/value mapping of the parameter name to more details about that parameter.

For example, there's one parameter for the enable method: name. Parameters can either go in the path or the URL query; the location property indicates where the client library should put the parameter.

There are many other properties describing the parameter, including the parameter data type (useful for strongly-typed languages), whether the parameter is required, and whether the parameter is an enum. See the reference documentation for this API for more details about these properties.

Parameter order

There are many ways for client libraries to structure their interfaces. One way is to have a method with each API parameter in the method signature. However, since JSON is an unordered format, it's difficult to know programmatically how to order the parameters in the method signature. The parameterOrder array provides a fixed parameter ordering for making requests. The array lists the name of each parameter in order of significance; it can contain either path or query parameters, but every parameter in the array is required.

Media upload

If a method supports uploading media, such as images, audio, or video, then the location and protocols supported for uploading that media are documented in the mediaUpload section. This section contains details about which upload protocols are supported, and information about what kinds of media can be uploaded.

The enable method doesn't contain a mediaUpload section. However, a typical mediaUpload section might look like the following:

"supportsMediaUpload": true,
"mediaUpload": {
  "accept": [
    "image/*"
  ],
  "maxSize": "10MB",
  "protocols": {
    "simple": {
      "multipart": true,
      "path": "/upload/storage/v1beta1/b/{bucket}/o"
    },
    "resumable": {
      "multipart": true,
      "path": "/resumable/upload/storage/v1beta1/b/{bucket}/o"
    }
  }
}

In the example above, the supportsMediaUpload property is a boolean value that determines if the method supports uploading media. If the value is true then the mediaUpload section documents the kinds of media that can be uploaded.

The accept property is a list of media-ranges that determine which mime-types are acceptable to upload. The endpoint shown in the example above will accept any image format.

The maxSize property has the maximum size of an upload. The value is a string in units of MB, GB or TB. In the example above, uploads are limited to a maximum size of 10 MB. Note that this value doesn't reflect an individual user's remaining storage quota for that API, so even if the upload is less than maxSize the client library should still be prepared to handle an upload that fails because of insufficient space.

The protocols section lists the upload protocols that a method supports. The simple protocol is simply POSTing the media to the given endpoint in a single HTTP request. The resumable protocol implies that the endpoint given in the path URI supports the resumable upload protocol. If the multipart property is true then the endpoint accepts multipart uploads, which means both the JSON request and the media can be wrapped together in a mutlipart/related body and sent together. Note that both simple and resumable protocols may support multipart uploads.

The path property is a URI Template and should be expanded just like the path property for the method, as outlined in the Compose a request section.

Media download

If a method supports downloading media, such as images, audio, or video, then that is indicated by the supportsMediaDownload parameter:

"supportsMediaDownload": true,

When downloading media you must set the alt query parameter to media in the request URL.

If the useMediaDownloadService property of the API method is true, insert /download before servicePath to avoid a redirect. For example, the download path is /download/youtube/v3/captions/{id} if the concatenation of servicePath and path is /youtube/v3/captions/{id}. It is recommended to construct media download URL with /download even when useMediaDownloadService is false.

Note: It is allowed for one API method to support both media download and upload. Request URL construction logic for media upload and download works independently and does not interfere with each other. As a result, such API method will have one /download/... url for media download and one /upload/... url for media uploading. However, one cannot do media upload and download in one single request.

Common parameters

The top-level Discovery document contains a parameters property. This section is similar to the parameters section for each method, however these parameters can be applied to any method in the API.

For example, the get and list methods of the Service Usage API can have a prettyPrint parameter in the request parameters, which will format the response for all those methods in a human-readable format. Here's a list of common parameters:

Parameter	Meaning	Notes	Applicability
`access_token`	OAuth 2.0 token for the current user.	One possible way to provide an OAuth 2.0 token.
`alt`	Data format for the response.	Valid values: `json`, `atom`, `csv`. Default value: varies per API. Not all values are available for every API.	Applies to all operations for all resources.
`callback`	Callback function.	Name of the JavaScript callback function that handles the response. Used in JavaScript JSON-P requests.
`fields`	Selector specifying a subset of fields to include in the response.	Use for better performance.
`key`	API key. (REQUIRED)	Required unless you provide an OAuth 2.0 token. Your API key identifies your project and provides you with API access, quota, and reports. Obtain your project's API key from the APIs console.
`prettyPrint`	Returns response with identations and line breaks.	Returns the response in a human-readable format if `true`. Default value: varies per API. When this is `false`, it can reduce the response payload size, which might lead to better performance in some environments.
`quotaUser`	Alternative to `userIp`.	Lets you enforce per-user quotas from a server-side application even in cases when the user's IP address is unknown. This can occur, for example, with applications that run cron jobs on App Engine on a user's behalf. You can choose any arbitrary string that uniquely identifies a user, but it is limited to 40 characters. Overrides `userIp` if both are provided. Learn more about capping usage.
`userIp`	IP address of the end user for whom the API call is being made.	Lets you enforce per-user quotas when calling the API from a server-side application. Learn more about capping usage.

Inline documentation

Each Discovery document is annotated with a number of description fields that provide inline documentation for the API. The description fields can be found for the following API elements:

API itself
OAuth scopes
Resource schemas
API Methods
Method parameters
Acceptable values for certain parameters

These fields are especially useful if you wish to use the Google APIs Discovery Service to generate human readable documentation for a client library—for example, JavaDoc.