Playground
Paste HTML and CSS, see it rendered by real Chromium in a couple of seconds. No signup, no card. The preview comes back at half resolution; buy a pack to render it at full size from your own account.
POST /v1/playground600x315 png, half resolution
This is the playground ceiling, not a watermark: nothing is removable.
Why it looks soft
The layout renders at the size you asked for, then the image comes back at half resolution: a 1200×630 layout is a 600×315 PNG. That is visibly soft on any retina screen and gets rejected as low resolution by LinkedIn's own inspector. It is enough to prove the HTML works, not enough to ship. A pack renders at full resolution from your own account, signed URLs included.