Google Docs, Slides and Drawings rolled out a convenient feature in June 2019 to preview link details. When you type and click a link in Docs, Google will automatically display the title, thumbnail and an excerpt of the link for you. It also converts the text part of link to the site title.

But, for schools, a coin has two sides. Given that students like sharing resources, the feature exposes potential risks for students to find violent, nudity or disturbing content. As the trick part, your network firewall is unaware of these links and failed to filter them because Google carries the data as the proxy for students.

Disable Link Preview Feature in Docs, Slides and Drawings
Link Preview feature in Docs is a red light for schools
Live Preview feature in Slides exposes potential risks to students
Live Preview feature in Slides exposes potential backdoor risks to find inappropriate contents

Schools found another issue of the link preview Youtube videos in Docs or Slides. If a student pastes a Youtube link on a Doc or Slide, clicks on the link, then a preview dialog pops up. Click the Open preview button in the dialog, then students can watch the videos in a separate preview window.

In Google Classroom's Stream page, students can add links to their posts. Google automatically loads a thumbnail and a title upon adding a link. These thumbnail requests are proxied by Google, so they may bypass your network firewall.

Link thumbnails in Google Classroom Stream
Link thumbnails in Google Classroom Stream


First of all, it's recommended to blacklist these inappropriate domains or links from your network firewall or content filtering solution. At least the students are not allowed to open these links in new tabs and see the whole page.

Then, make sure you have installed Safe Doc correctly. It's a chrome extension that blocks certain inappropriate features in Google Workspace for Education to protect your students. If you have yet to install Safe Doc, please get a 30 days trial.

When Safe Doc is deployed in your PC or your students' Chromebooks, without configuration, it blocks the link preview feature in Docs, Slides and Drawings. You will see the link pop up is gone. The actions buttons that Safe Doc do not block are copying link, editing link and un-linking.

Disable Link Preview Feature in Docs, Slides and Drawings
Link Preview feature removed by Safe Doc

The blocking strategy in feature-level with Safe Doc and network filtering protects your students from finding harmful contents.

To configure Safe Doc to block the link preview, set BlockDocLinkPreview policy to true. Otherwise, the value to false. See more details in Safe Doc Configuration.

"BlockDocLinkPreview": {
  "Value": true

You may also like