# Package Version Header

Specifies the version of each package referenced by a client. A package version is a number that identifies the set of components and behavior contained in a package. This header can also be used to specify a package version when making calls to an Apex REST web service.

The Package Version header can be used with the following resources: Describe Global, sObject Describe, sObject Basic Information, sObject Rows, sObject Layouts, Query, QueryAll, Search, and sObject Rows by External ID.

## Header Field Name and Values

- **Field name and value**: `x-sfdc-packageversion-[namespace]: xx.x`, where `[namespace]` is the unique namespace of the managed package and `xx.x` is the package version.
- **Example**: `x-sfdc-packageversion-clientPackage: 1.0`