ThumbLens — Thumbnail Preview & A/B Tester

Free. Preview your thumbnail in a realistic simulated feed — home, search, sidebar and mobile — before you upload.

A blank canvas lies. Your thumbnail never appears alone — it appears in a crowded feed, at small size, next to eleven other videos fighting for the same click. ThumbLens shows you that view before you upload. Drop in an image, type your title, and see it placed in a realistic simulated feed. WHAT YOU GET — all of it, free • Home feed — your thumbnail in a grid of competing videos • Search results — the wide layout, with real title truncation • Suggested sidebar — the compact column beside a playing video • Mobile — a phone-sized frame, where most impressions actually happen • A/B compare — up to four versions in the same feed slot, only the image changing • Squint test — progressive blur to check whether it still reads at a glance • PNG export — send a client or collaborator the mockup, not a description • Saved previews, kept locally • Light and dark No account, no limits, no ads. WHY A SIMULATED FEED The preview is drawn by ThumbLens itself, not scraped from any website. That is why it works offline, needs no access to your browsing, and cannot break when a platform changes its markup. It is an approximation of a generic video feed, reviewed on a monthly parity cycle. PRIVACY Your images and titles never leave your browser. There is no account, no upload and no analytics. While you use it the extension makes no network requests at all; the only page it ever opens on our site is the feedback page shown when you uninstall. It asks for one permission (storage) and no host access — it cannot read the pages you visit. This is an independent tool, not affiliated with, endorsed by, or produced by YouTube or Google.