# Free YouTube Thumbnail Preview Tool

> Drop in a thumbnail and see exactly how it looks in the YouTube home feed, sidebar, search results and mobile, in light and dark mode, at true pixel sizes. Free, private, nothing uploaded.

Free, no account required. Runs entirely in your browser — nothing is uploaded.

## How to use it

1. **Drop in your thumbnail.** Drag a JPG or PNG onto the page, or click to choose one. It stays in your browser and is never uploaded.
2. **Check every placement.** The same image is rendered at home feed, sidebar suggestion, search result and mobile sizes, in both light and dark mode.
3. **Fix what breaks.** If the text is unreadable in the sidebar, it is unreadable where most impressions happen. Go back and make it bigger.

## Why 1280×720 is the wrong size to judge a thumbnail at

Almost nobody sees your thumbnail at 1280 pixels wide. A sidebar suggestion renders at roughly 168–246 px across, a mobile home feed card at around 320–400 px, and a search result somewhere between. You design at full size and the audience sees a postage stamp.

This is the single most common reason a thumbnail underperforms: five words of 40px text look bold and confident in the editor, and dissolve into grey mush at sidebar size. Previewing at the real size takes ten seconds and catches it every time.

## Dark mode is the majority case

Most YouTube viewing happens in dark mode, where a thumbnail with dark edges bleeds into the page and loses its outline. A light border, a bright rim light or a high-contrast background is what keeps the frame distinct.

The preview shows both. If your thumbnail disappears into one of them, that is worth knowing before you upload rather than after.

## Frequently asked questions

### Is my image uploaded anywhere?

No. Everything happens in your browser — the file is read locally and rendered to a canvas. Nothing is sent to a server, which is also why the tool works with no account and no limit.

### What size should I test at?

Test the image you are actually going to upload, at 1280×720 or larger. The tool scales it down to each real placement size, which is the point: you are checking that it survives the shrink.

### What is the smallest size a YouTube thumbnail appears at?

Sidebar suggestions are the tightest common placement at roughly 168–246 px wide. If your text is legible there, it is legible everywhere else.

### Does this tell me whether my thumbnail will get clicks?

No tool honestly can — click-through depends on the title, the audience and what it is competing against in that feed. What this shows is whether your thumbnail is legible and distinct at real sizes, which is the floor you have to clear before anything else matters.

---

Use it at https://thumbn.so/thumbnail-preview — part of [Thumbn](https://thumbn.so), AI thumbnail generator for YouTube, TikTok and Reels.