Typically they'll basically be a markup resource. IE: I have a ton of documents in one format, and I need them to be translated to clean HTML.

The other thing that may be needed in this position is actual content development skills, ie: writing. You could be responsible for doing blog posts, pages on websites, marketing copy, etc.

"Web content developer" would also be the lowest paid position in an agency typically. The salary ladder goes "web content|web maintenance/support" > "front-end|SEO|social/marketing" > "back-end|fullstack" > "management" > "ownership" in my experience.