/thumbnails API response returns "no-cache" policy, no Etag

Hi Matt, it sounds like you already have the right idea here. You should use the Dropbox API concepts to keep track of this, instead of HTTP caching rules. That is, you can use the "rev" value, e.g., from /metadata or /delta, to check if the contents have changed. If the rev value hasn't changed for a file, you know the contents haven't changed, and therefore your saved thumbnail for that rev is still valid. If the rev has changed, that means the file contents have changed, so you should call /thumbnails again to get the latest thumbnail.