Add this script where you want the date to appear. After loading, the widget updates without making additional network requests.

<script src="https://todayjuliandate.com/widget.js"></script>

With options:

<script src="https://todayjuliandate.com/widget.js"
        data-format="full"
        data-theme="auto"></script>

Attribute	Default	Values
data-format	yyyyddd	yyyyddd · yyddd · ddd · jd · mjd · full
data-theme	auto	auto · light · dark
data-tz	local	local · utc
data-link	true	Set to false to drop the credit link
data-target	—	CSS selector to render into, instead of in place

If a script tag is not allowed where you need it, embed the standalone page instead:

<iframe src="https://todayjuliandate.com/embed/"
        width="320" height="150" frameborder="0"
        title="Today's Julian date"></iframe>

Licence

The widget is free for any use, including commercial. No attribution is required, though a link back to todayjuliandate.com is appreciated.

Julian Date Widget