System parameters
Google's API platform provides a set of common functionality to all Google APIsbuilt using the platform. In order to use and control such functionality,the platform pre-defines a special set of request parameters calledsystem parameters. These parameters are available across all Google REST APIsand gRPC APIs. A system parameter can be specified either using an HTTP queryparameter or an HTTP header. For Google gRPC APIs, only HTTP headers aresupported.
Most users will not need to use these parameters directly. However, they areoften used by Google-providedclient libraries. If you need to writecustom code to access Google APIs directly, the system parameters can beuseful in cases such as controlling JSON pretty-printing or specifying API Keys.
HTTP Mapping
For HTTP requests, system parameters are sent as URL query parameters orHTTP request headers. For example, if you have a system parameter$foo, it'ssent as?$foo=xxx in the URL, or?%24foo=xxx if URL-encoded. See thetable below for details.
$ name prefix is added to avoid conflicting with normal requestparameters.gRPC Mapping
ForgRPC requests, system parameters are sent as HTTPrequest headers with keys in lowercase. See the table below for details.
Definitions
The following table lists all system parameters and their definitions.
| URL Query Parameter | HTTP/gRPC Header | Description |
|---|---|---|
Authorization | Authentication credentials. SeeAuthentication overview for details. | |
$alt,alt | Alternative response format. Supported values arejson (default),media,proto,sse (JSON streams). | |
$.xgafv | JSON error format. Supported values are1,2 (default). The error format1 should only be used byGoogle API Client Libraries. | |
$callback,callback | JSONP callback parameter. | |
$ct | Content-Type | HTTP Content-Type request header override. |
$fields,fields | X-Goog-FieldMask | FieldMask used for response filtering. If empty, all fields should be returned unless documented otherwise. |
X-HTTP-Method-Override | The intended HTTP method for the request. Some network proxies don't accept all HTTP methods. | |
$key,key | X-Goog-Api-Key | Google API key. See https://cloud.google.com/docs/authentication/api-keys for details. |
passwd,password | Reserved to prevent putting passwords in URLs. | |
$prettyPrint,prettyPrint | Pretty-print JSON response. Supported values aretrue (default),false. | |
quotaUser | X-Goog-Quota-User | A pseudo user identifier for charging per-user quotas. If not specified, the authenticated principal is used. If there is no authenticated principal, the client IP address will be used. When specified, a valid API key with service restrictions must be used to identify the quota project. Otherwise, this parameter is ignored. |
$outputDefaults | Force to output proto default values for JSON responses. | |
$unique | Unique query parameter to disable request caching. | |
X-Goog-Api-Client | API client identification. The value is a space-separated list ofNAME "/" SEMVER strings, where theNAME should only contain lowercase letters, digits, and "-", and theSEMVER should be a semantic version string. For example: X-Goog-Api-Client: python/3.5.0 grpc-google-pubsub-v1/0.1.0-beta2 linux/2.7.0. | |
X-Goog-Request-Reason | Contains a reason for making the request, which is intended to be recorded in audit logging. An example reason would be a support-case ticket number. For audit logs, the characters in the reason determine whether the reason is base64 encoded before being attached to the log entry. Reasons that include only letters, digits, and spaces are retained in plain text. Reasons that include other characters are base64 encoded. | |
$userProject | X-Goog-User-Project | A caller-specified project for quota and billing purposes. The caller must haveserviceusage.services.use permission on the project. |
X-Server-Timeout | Timeout (in seconds, float value) for the server to finish processing the request. This system param only applies to REST APIs for which client-side timeout is not applicable. | |
x-goog-request-params | Passing additional parameters for gRPC requests in URL query format. For example: x-goog-request-params: service=pubsub.googleapis.com&release=2021-11-01r0. |
Changelog
- 2021-11 Published documentation for
x-goog-request-params. - 2021-02 Published documentation for
quotaUser. - 2020-07 Deprecated OAuth 2.0 query parameters.
- 2019-10 Introduced
X-Server-Timeoutsystem parameter. - 2017-10 Introduced
X-Goog-User-Projectsystem parameter.
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Last updated 2026-02-19 UTC.