LinkedIn truncates a post after roughly 200 characters on mobile and shows a "see more" link. Everything above that cut is the only thing most people ever read, so the preview above renders your draft at the same break point. Line breaks are the other thing worth checking: LinkedIn collapses some whitespace that looks fine in your editor, and a post that reads as three tight paragraphs in a text field can arrive as one wall.
A preview only helps once there's a draft. If you're staring at the empty box, generate a post with AI first — give it a topic and it writes a full draft you can paste straight back into this preview, adjust the hook, and check the mobile cut before you publish.
No. This page is a renderer, not a publisher — your text stays in the browser and nothing is sent to LinkedIn. When you're happy with the draft, copy it across yourself, or use ContentIn if you want drafting, scheduling and publishing in one place.