The three checks every thumbnail needs
A thumbnail can fail in three separate ways, and each needs a different check. Passing one doesn't tell you anything about the other two.
- Design check. Is there one clear focal point, readable text, and strong contrast? Upload your image above for an AI check with specific fixes.
- File check. Is it the right shape, format, and size? Use the thumbnail size checker.
- Feed check. Does it still work small, next to other videos? Use the thumbnail preview tool.
A 12-point pre-upload checklist
Go through these in order. Stop and fix anything you answer "no" to.
Design
- Can you say what the thumbnail is about in one word?
- Is there a single, clearly largest subject?
- Is there strong contrast between the subject and the background?
- Is the text three or four words, in a heavy font with an outline?
- Does the text add something the title doesn't already say?
- Does the video deliver what the thumbnail suggests?
File
- Is it 16:9?
- Is it at least 640 pixels wide, and ideally 1280 by 720 or larger?
- Is it a JPG or PNG?
- Is it under 2 MB if you're uploading from the mobile app, or 50 MB from a computer?
Feed
- Can you read everything when it's about the size of a postage stamp?
- Is the bottom-right corner, where YouTube shows the video length, clear?
The current numbers come from YouTube's custom thumbnail help page (checked September 2026). Our size guide explains each one.
How to check a thumbnail that's already live
If a video is underperforming, check it in this order:
- Look at the published version, not your original file, and check it isn't blurry or cropped.
- Shrink it to feed size and run the design check above.
- Compare the video's impressions click-through rate with your other recent videos. Our guide to checking thumbnail CTR in YouTube Studio shows where to find it.
- If you change the thumbnail, change one thing at a time and measure the result. See how to change a YouTube thumbnail.
What the checker can't tell you
- Your real click-through rate. No pre-publish tool can. It can catch problems, not predict clicks.
- Whether your topic is in demand. A perfect thumbnail can't rescue a video nobody is searching for.
- Policy problems. Misleading images and borrowed artwork can cause trouble even when the design is strong. See thumbnail mistakes that risk your channel.
Checker or rater?
The thumbnail rater goes deeper on the design itself, with separate scores for visual hierarchy, readability, and clickability. The checker is the wider routine that also covers the file and the feed. Use the rater to improve the design, then the checker as your last step before you upload.
Frequently asked questions
What should I check before uploading a YouTube thumbnail?
Check three things: the design (one clear focal point, readable text, strong contrast), the file (16:9, JPG or PNG, under the size limit for your device), and how it looks small, in a feed next to other videos.
Can I check a thumbnail that is already live?
Yes. Upload a copy of the image, or a screenshot cropped to the thumbnail, and run it through the same checks. Also compare the video's click-through rate in YouTube Studio with your other recent videos.
Does the checker tell me if my thumbnail follows YouTube's rules?
It checks the technical limits, such as format, ratio, and file size. It can't judge policy questions such as misleading content. Read YouTube's current policies for that, and see our guide to thumbnail mistakes that can put a channel at risk.
Is it free?
Yes. The design check gives you five free runs a day, and the size checker and preview tool are free to use.
Is my image stored?
The size checker and preview tool run in your browser and never upload your image. The design check sends the image to the AI provider to generate feedback and doesn't save it.