Manage file metadata

This document covers important considerations for naming files and working with metadata like indexable text and thumbnails. To insert and retrieve files, see the files resource.

Metadata overview

In the Google Drive API, the files resource represents the metadata. Unlike APIs where metadata is a sub-object, the Drive API treats the entire files resource as metadata. You can access the metadata directly through the get or list methods on the files resource.

By default, the get and list methods return only a partial set of fields. To retrieve specific data, you must define the fields system parameter in your request. If omitted, the server returns a default subset of fields specific to the method. For example, the list method returns only the kind, id, name, mimeType, and resourceKey fields for each file. To return different fields, see Return specific fields.

Additionally, metadata visibility depends on the user's role on the file. The permissions resource doesn't determine a user's allowed actions on a file or folder. Instead, the files resource contains a collection of boolean capabilities fields. The Google Drive API derives these capabilities from the permissions resource associated with the file or folder. For more information, see Understand file capabilities.

The Drive API offers two restricted metadata scopes: drive.metadata and drive.metadata.readonly. The drive.metadata scope lets you view and manage file metadata, while drive.metadata.readonly is read-only. Both strictly prohibit access to file content. For more information, see Choose Google Drive API scopes.

Finally, always verify your logic regarding permissions and scopes. For example, a user might own a file with full permissions, but the Drive API will block attempts to modify or download the file if your app only has the drive.metadata.readonly scope.

Specify file names and extensions

Apps should specify a file extension in the name) property when inserting files with the Google Drive API. For example, an operation to insert a JPEG file should specify something like "name": "cat.jpg" in the metadata.

Subsequent GET responses can include the read-only fileExtension property populated with the extension originally specified in the name property. When a Google Drive user requests to download a file, or when the file is downloaded through the sync client, Drive builds a full filename (with extension) based on the name. In cases where the extension is missing, Drive attempts to determine the extension based on the file's MIME type.

Save indexable text

Drive automatically indexes documents for search when it recognizes the file type, including text documents, PDFs, images with text, and other common types. If your app saves other types of files (such as drawings, video, and shortcuts), you can improve the discoverability by supplying indexable text in the contentHints.indexableText field of the file.

Indexable text is indexed as HTML. If you save the indexable text string <section attribute="value1">Here's some text</section>, then "Here's some text" is indexed, but "value1" isn't. Because of this, saving XML as indexable text isn't as useful as saving HTML.

When specifying indexableText, also keep in mind:

  • The size limit for contentHints.indexableText is 128 KB.
  • Capture the key terms and concepts that you expect a user to search.
  • Don't try to sort text in order of importance because the indexer does that efficiently for you.
  • Your application should update the indexable text with each save.
  • Make sure the text is related to the file's content or metadata.

This last point might seem obvious, but it's important. It's not a good idea to add commonly searched terms to force a file to appear in search results. This can frustrate users, and might even motivate them to delete the file.

Upload thumbnails

Drive automatically generates thumbnails for many common file types, such as Google Docs, Sheets, and Slides. Thumbnails help the user to better identify Drive files.

For file types that Drive can't generate a standard thumbnail for, you can provide a thumbnail image generated by your application. During file creation or update, upload a thumbnail by setting the contentHints.thumbnail field on the files resource.

Specifically:

  • Set the contentHints.thumbnail.image field to the URL and filename safe base64-encoded image (see RFC 4648 section 5).
  • Set the contentHints.thumbnail.mimeType field to the appropriate MIME type for the thumbnail.

If Drive can generate a thumbnail from the file, it uses the automatically generated one and ignores any you might have uploaded. If it can't generate a thumbnail, it uses the one you provide.

Thumbnails should adhere to these rules:

  • Can be uploaded in PNG, GIF, or JPG formats.
  • The recommended width is 1600 pixels.
  • The minimum width is 220 pixels.
  • The maximum file size is 2 MB.
  • They should be updated by your application with each save.

For more information, see the files resource.

Retrieve thumbnails

You can retrieve metadata, including thumbnails, for Drive files. Thumbnail information is housed in the thumbnailLink field of the files resource.

Return a specific thumbnail

The following code sample shows a get method request with multiple fields as a query parameter to return the thumbnailLink metadata for a specific file. For more information, see Return specific fields for a file.

GET https://www.googleapis.com/drive/v3/files/FILE_ID?fields=id,name,mimeType,thumbnailLink

Replace FILE_ID with the fileId of the file that you want to find.

If available, the request returns a short-lived URL to the file's thumbnail. Typically, the link lasts for several hours. The field is only populated when the requesting app can access the file's content. If the file isn't shared publicly, the URL returned in thumbnailLink must be fetched using a credentialed request.

Return a list of thumbnails

The following code sample shows a list method request with multiple fields as a query parameter to return the thumbnailLink metadata for a list of files. For more information, see Search for files and folders.

GET https://www.googleapis.com/drive/v3/files/?fields=files(id,name,mimeType,thumbnailLink)

To restrict the search results to a specific file type, apply a query string to set the MIME type. For example, the following code sample shows how to limit the list to Google Sheets files. For more information on MIME types, see Google Workspace and Google Drive supported MIME types.

GET https://www.googleapis.com/drive/v3/files/q=mimeType='application/vnd.google-apps.spreadsheet'&fields=files(id,name,mimeType,thumbnailLink)