Files existing image, video, or audio assets into a folder, like dropping media on a folder in the web app. Target it with folderId or folderPath (a missing folderPath is created); omit both for the top level. An asset already in the tree moves; a new item takes the asset's name, made unique within the folder. Assets from elsewhere in the team are linked into the session without changing where they were created. Write text with POST /workspace/documents instead. The change shows up in the Yapper web app and is recorded with the API key or MCP client that made it; the in-app Yapper agent in that session is told about it on its next turn. Free. Uses the processes:write scope.