While users can create rich link previews in their posts using oneboxes (See: Create rich link previews with Onebox), there are some controls available to site administrators, and sometimes when links do not preview as expected, it can be helpful to do a bit of troubleshooting to understand why.
Admin configuration
Site administrators can control many of the onebox settings in the site setting section. To see available settings search for onebox.
Notable settings are:
post onebox maxlengthto control how much text is included in a oneboxenable inline onebox on all domainswhich can enable inline oneboxes, eg converting the text https://en.wikipedia.org/wiki/Fun_(band)` in a post to Fun (band) - Wikipedia based on the HTML page title. This is now on by default.blocked onebox domainsto disable onebox on certain domains
tesst document - Google Drive
Troubleshooting
Behind the scenes, the onebox feature visits the destination page and checks for Open Graph or oEmbed tags, including:
- site address
- title
- feature image
- description (mandatory)
- product price
Please note that Discourse does require the description tag to be present and contain enough text to summarize the page, or the target link will not onebox.
If Onebox is not working as expected, please check the following:
- Test your site by pasting the link into iFramely; check that the target is using correct OpenGraph or oEmbed meta tags for content. And remember the description text is required in Discourse!
- Verify that the onebox request to the target website has not been blocked by
user-agent. Some WordPress hosts frequently block “unknown” user agents. - If an internal link is not displayed as Onebox, make sure it is not in a secure category. For security reasons, internal links only Onebox in public categories or in the same category.