Best tag for image description?

[Joanna Carter]

I want users of my app to be able to write a "description" or "narrative" for a given picture.

I was primarily looking at the XMP section. Can someone advise me as to the most commonly used tag?

[StarGeek]

Use Description

Take a look at the IPTC Photo Metadata Standard 2019.1 spec for ideas as to what tags are supposed to be used for what purpose.  It's a dry read, but the description, help text, and user notes for each tag give the basic idea of a tag's purpose.  Then below, it gives you the XMP and IPTC IIM tag name, though you might have to look at the XMP tags page or the IPTC tags page to get the exact exiftool name.

For example, for Copyright Notice, it says

In this case, you would use Country (or more specifically XMP:Country or XMP-Photoshop:Country) for the XMP tag and Country-PrimaryLocationName (or IPTC:Country-PrimaryLocationName) for IPTC IIM.