Markdown is a text-to-HTML conversion tool for web writers. Markdown allows you to write using an easy-to-read, easy-to-write plain text format, then convert it to structurally valid HTML.
Sketchfab supports Markdown in model descriptions and Annotations.
Primary Markdown Syntax
These are the features most relevant to Sketchfab models.
Images

Will produce
Optionally, you can add alt text and a title (important for SEO and accessibility), like this:

Links
This is [an example](http://example.com/ "Title") inline link.
[This link](http://example.net/) has no title attribute.
This is [an example][id] reference-style link.
Other stuff goes here...
[id]: http://example.com/ "Optional Title Here"
Will produce an example link.
You can make an image that is a link by combining the link code with the image code. Use the image code instead of text:
[](http://example.com)
Videos
While you can link to a video hosted elsewhere (as described above), you cannot produce a video within your model's description or Annotations by using Markdown.
If you'd like to build a more customized experience with features like embedded videos, it's possible to do on your own website using the Viewer API.
Emphasis
*single asterisks*
_single underscores_
Will produce italic text
**double asterisks**
__double underscores__
Will produce bold text
Titles
This is an H1
=============
This is an H2
-------------
# This is an H1
## This is an H2
###### This is an H6
Lists
Unordered
* Red
* Green
+ Blue
- Yellow
Will produce
- Red
- Green
- Blue
- Yellow
Ordered
1. First item
2. Second item
1. Third item
(The number before the period has no effect on the actual order, it just needs to be a number)
Will produce
- First item
- Second item
- Third item
Other Markdown Syntax
A lot of other Markdown features are supported, but they may not be very useful in the context of Sketchfab models. See this documentation for details:
It's also supported in Help Center comments, although the implementation may not be identical.