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Thumbnail Preview Tool

A thumbnail that looks great full-screen in your editor can fall apart at the 168 pixels a viewer actually sees. This thumbnail preview tool renders your image at real display sizes — large grid, medium list and tiny sidebar — beside realistic competing cards, so you find out before you post, not after. Runs entirely in your browser.

  • 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. Add your thumbnail

    Drop in the image you are considering — add up to three more versions if you are deciding between drafts.

  2. Check every size

    Switch between grid, search-list, sidebar and mobile views. The sidebar view is the truth serum: if your text is unreadable there, it is unreadable to most viewers.

  3. Refine and re-test

    Fix contrast or oversized text in your editor, re-drop the file and compare the before and after side by side.

Questions people ask

Why preview a thumbnail instead of just posting it?

Because you design at 1280×720 but viewers see 168–360 pixels. Details, thin fonts and subtle colour differences disappear at display size; a 30-second preview catches that before the post goes live.

What makes a thumbnail readable at small sizes?

Three or fewer words in thick type, one clear subject, and strong contrast between subject and background. If you squint at the sidebar preview and still get the idea, it works.

Can I compare several drafts at once?

Yes — up to four render simultaneously in the same layout with the same title, so the comparison is fair. Remove and re-add drafts as you iterate.

Does dark mode really change how a thumbnail reads?

Often, yes — a dark thumbnail that pops on a white page can merge into a dark UI. The dark/light toggle here shows both, since roughly half of viewers browse in dark mode.

Are my images uploaded when I preview them?

No — the previews are built in your browser from the local file. Nothing is transmitted, so unreleased artwork stays private.

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.