Thumbnailr › YouTube thumbnail tester
Free YouTube thumbnail tester and previewer
See your thumbnail the way viewers will: tiny, on a phone, next to other videos. Click check scores it for readability, and feed test puts it in a realistic mock feed. Free, no sign-up, nothing uploaded.
Why test a thumbnail before you upload?
You design a thumbnail at full size on a big screen, but most viewers see it at around 160 to 360 pixels wide, often on a phone, surrounded by other thumbnails. Text that looked huge in the editor can turn into a smudge. A quick pre-upload test catches that before your video goes live with it.
Click check: a 0–100 readability score
Click check runs while you edit and scores the design out of 100. It renders small copies of your thumbnail (at home-feed and search sizes) and checks nine things:
| Check | What it looks for | Points |
|---|---|---|
| Readable on phones | Text big enough to read at phone feed size. | 20 |
| Text stands out | Enough contrast between text and what's behind it. | 15 |
| Clear of the time badge | Nothing important in the bottom-right corner, where YouTube shows the video length. | 12 |
| Few words | Short text, ideally two to four words. | 10 |
| Face or subject | One clear focal point. | 10 |
| Contrast & colour | A design that doesn't look flat or washed out. | 10 |
| Not too busy | Not so many elements that nothing stands out. | 10 |
| Inside the safe area | Key elements kept away from the edges. | 8 |
| Adds to the title | Text that adds something instead of repeating the title. | 5 |
How it’s scored. A passed check earns its full points, a warning earns half and a fail earns none. Checks that don’t apply (for example, no text) are left out, and the total is scaled to 100. The editor shows the points for each check. Text size and contrast are measured on small renders; “Contrast & colour” and “Not too busy” are rules of thumb.
Each tip links to the layer that caused it, so you can click a tip and fix it. Open click check on your current design.
What the score is, and isn't. Click check is a guide based on common thumbnail advice. It is not a click-through rate (CTR) predictor: no tool can know your real CTR before real viewers see the video. Use it to catch obvious problems, then let YouTube's numbers decide.
Feed test: preview it in a mock YouTube-style feed
Feed test places your thumbnail in a generic, unbranded feed next to other videos so you can judge it in context. You can:
- Switch between dark and light mode, and between desktop and phone layouts.
- See it at home grid, search list and sidebar sizes.
- Add your own title and channel name so the preview matches what viewers will read.
- Add up to five comparison images, such as competitors' thumbnails or a video link you import, then shuffle the feed to see whether yours still jumps out.
- Run an A/B view against a saved version B of your own design.
Comparison images stay in your browser's storage and are never uploaded. Open the feed test.
Compare two versions after you publish
Pre-upload testing narrows things down; real viewers settle it. YouTube Studio has a built-in “Test & compare” feature on desktop that lets you upload up to three thumbnails for one video. According to YouTube Help, it shows them to viewers and picks a winner by watch time. A practical routine:
- Make two or three genuinely different ideas in Thumbnailr (different face, words or colour, not tiny tweaks).
- Use click check and feed test to drop the weakest.
- Upload the finalists with Test & compare in YouTube Studio and let it run.
- Keep notes on what wins so your next thumbnail starts from a better guess.
A quick checklist before you hit publish
- Can you read the words at phone size in the feed test?
- Is the bottom-right corner clear for the time badge?
- Does it still stand out in light mode as well as dark?
- Does the text add to the title rather than repeat it?
- Is the file the right size? See the YouTube thumbnail size guide.
Making gaming videos? Start from a gaming layout that already passes most of these checks.
FAQ
Is the thumbnail tester free?
Yes. Click check and feed test are both included in Free mode, with no account and no limit on how often you use them.
Can it predict my click-through rate?
No. Click check is a readability guide based on common thumbnail advice, not a CTR prediction. Real CTR depends on your audience, title and topic, so use YouTube Studio's analytics and Test & compare for real results.
Can I test a thumbnail I already made somewhere else?
Yes. Drop your finished image onto the canvas as a layer and the click check and feed test will work on it like any other design.
Are my images uploaded?
No. The checks run in your browser, and comparison images are kept in your browser's storage on your device.
Ready to make yours? It's free, with no sign-up.