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YouTube Thumbnail Tester

This YouTube thumbnail tester (and checker) shows your thumbnail exactly where it will live — home grid, search results, suggested sidebar and mobile — with your real title and channel name, in dark and light mode. Upload up to four candidates to compare side by side, and get an automatic warning if a file is over 2 MB or not 1280×720. Everything stays in your browser; nothing is fetched from or sent to YouTube.

  • Nothing you type leaves this page
  • Works offline once loaded
  • Free forever, no signup
Drop 1–4 thumbnail candidates here Ideally 1280×720 JPG/PNG under 2 MB — checked automatically, never uploaded Converting the iPhone photo (HEIC) to JPEG…
Preview as

Simulated preview — not affiliated with YouTube. Compare the candidates side by side below.

Candidate {{ c.id }} · {{ c.width }}×{{ c.height }}
Thumbnail candidate
{{ truncate(title, 60) }} {{ channel }} · 12K views · 3 hours ago
{{ placeholderTitles[n] }} Sample channel · 8K views · 1 day ago
Thumbnail candidate
{{ truncate(title, 90) }} 12K views · 3 hours ago {{ channel }}
{{ placeholderTitles[n + 2] }} 21K views · 2 days ago Sample channel
Thumbnail candidate
{{ truncate(title, 50) }} {{ channel }} 12K views
{{ placeholderTitles[n - 1] }} Sample channel 5K views

At this size most viewers decide — if the text on your thumbnail is unreadable here, simplify it.

Thumbnail candidate
{{ truncate(title, 70) }} {{ channel }} · 12K views · 3h ago
{{ placeholderTitles[4] }} Sample channel · 9K views · 5h ago

How to use this tool

  1. Upload your candidates

    Add one to four thumbnail images and type the video title and channel name you plan to use.

  2. Flip through the contexts

    Preview each candidate in the home grid, search results, suggested sidebar and mobile layouts, in dark or light mode.

  3. Pick the winner

    Judge them side by side — pay special attention to the small sidebar size, where most real impressions happen — and fix any size warnings before uploading to YouTube.

Questions people ask

How can I preview my YouTube thumbnail before uploading?

Upload the image here and it is rendered inside simulated home, search, sidebar and mobile layouts with your title and channel name — no YouTube account needed and nothing touches your channel.

How do I A/B test two thumbnails for free?

Add both candidates and they render side by side in the same context with the same title, so the only variable is the thumbnail. Check them at sidebar size especially — that is where weak thumbnails die.

What is the correct YouTube thumbnail size?

1280×720 pixels (16:9) and under 2 MB, as JPG, PNG, GIF or WebP. This tool checks every uploaded file against both rules and warns you immediately if one fails.

Why does my thumbnail look bad when it is small?

Most impressions happen at under 200 pixels wide — sidebar suggestions render around 168px. Thin text, busy detail and low contrast all vanish at that size; the sidebar preview here is the honest test.

Does this tool fetch anything from YouTube?

No — the previews are hand-built lookalike layouts, the placeholder videos are fake, and the page makes no request to youtube.com at all. It is not affiliated with YouTube; your images stay on your device.

Does the title truncation match real YouTube?

Yes — titles clamp to two lines in the grid layouts and shorter one-to-two line limits in the sidebar, mirroring how YouTube cuts titles, so you can check whether your keyword survives the ellipsis.

Related tools

Free because it costs us nothing to run: your browser does the work, not our servers. Made by Dynamb Technologies — we build software for businesses.