A Claude project usually lives as a markdown file — text instructions that Claude reads and follows.
An HTML artifact is different. It's a fully interactive tool that Claude builds for you — with buttons, dropdowns, input fields, and a generate button. You open it in your browser and use it like an app.
Same Claude brain underneath. But instead of copy-pasting your way through a conversation, you pick your situation, fill in a few fields, and hit generate.
The insight (credit to Thariq from the Claude Code team, whose article sparked this): almost anything Claude can read, HTML can display and interact with. Markdown forces Claude to dumb down how it shows you things. HTML lets it actually build something useful.