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Apply this tool to one or many images locally in your browser.
Drop image(s) here or click to browse
Editor & live preview appear below once you add an image.
Reviewed 2026-08-15
Free Generate Thumbnails – how it works
Generate Thumbnails processes image files locally in your browser. It sits in the opentools Web & Design collection and is built on the browser's canvas and codec APIs, so the work happens on your own device instead of on a server you have to trust with the file.
Everything runs inside the current browser tab. The image on your device is read, never uploaded — the tool writes a separate output for you to inspect and download. No account, no queue, and no watermark on the result.
Decoding depends on the browser. Unusual format variants — CMYK JPEGs, 16-bit PNGs, or exotic TIFF flavours — may not render identically in every browser. Use a recent desktop build of Chrome, Firefox, Safari, or Edge for the widest format support and the most headroom on large files.
How to use Generate Thumbnails online
- Add your image. Drag one or more images into the drop zone, or click to browse. HEIC, TIFF, AVIF, and SVG inputs decode through the browser where supported.
- Set up the generate thumbnails options. Set the options that matter for this tool — dimensions, quality, colour, or output format. A live preview updates as you change values, so you can judge the result before exporting.
- Run it and download. Run the tool, compare the preview against the original, then download a single file or every result at once.
When to use it
- Complete a generate thumbnails task without installing a desktop application.
- Handle a confidential image without sending it through a third-party upload form.
- Do a quick one-off generate thumbnails job without installing an image editor.
Known limitations
- Decoding depends on the browser. Unusual format variants — CMYK JPEGs, 16-bit PNGs, or exotic TIFF flavours — may not render identically in every browser.
- Large inputs are bounded by the memory a single browser tab can claim — roughly 50 MB for image work on a typical laptop, and considerably less on phones.
- Check the output before you discard the original, especially for lossy or rasterising operations where the change cannot be undone.
Frequently asked questions
Is Generate Thumbnails free to use?
Yes — no usage limits, no paywalled settings, no account, and no watermark on the output. opentools is funded as a free utility, not a freemium trial.
Are my image files uploaded when I use Generate Thumbnails?
No. The processing pipeline is the browser's canvas and codec APIs running inside your browser tab, so the image never leaves your device. Anonymous page analytics still load, but they carry no file content.
Does Generate Thumbnails change my original file?
No. A web page cannot silently overwrite files on your disk. The tool reads your input and produces a new file that you choose to download, leaving the source untouched.
Can I run Generate Thumbnails on a phone or tablet?
Yes, in any modern mobile browser. Speed and the largest workable image depend on the device's free memory, so keep mobile jobs small and expect desktop to handle the heavy cases.
Does Generate Thumbnails work offline?
An internet connection is needed the first time so the page and its engine can load. Image processing uses APIs that ship with the browser, so after the page loads no further network access is needed.
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