Local vs Upload Converters: What Actually Differs
Most online converters copy your file to a server. Ours run in your browser. Here is what that changes, including where uploading is the better choice, and a test you can run yourself.
Time a real conversion in your browser
Encodes a 12-megapixel test image (the size of a typical phone photo) to JPEG on your own processor, then works out how long uploading the same file would take at your connection speed.
No upload
Your file is processed on your device. You can confirm it with the steps below.
No upload wait
Large files skip the upload and download, which is often the slowest part on a home connection.
Your device does the work
Quick for images and documents. Long videos convert faster on a server or in native software.
Side by side
| Aspect | In your browser (ConvertStuff) | Upload converters |
|---|---|---|
| Where the file goes | Read into your browser's memory and processed on your device. | Copied to the vendor's servers and processed there. |
| How long it is kept | Not stored by us at all. Closing the tab releases it. | Each vendor sets its own window, e.g. Smallpdf 1 hour, iLovePDF 2 hours, FreeConvert 8 hours, CloudConvert up to 24 hours, TinyPNG up to 48 hours. |
| Waiting before work starts | None. The file is already on your device. | The upload, which depends on file size and your upload speed. Try the test above. |
| Processing speed | Limited by your device. Fine for images, text and PDFs; video is noticeably slower than native software. | Server hardware, usually faster for heavy jobs such as long videos. |
| Limits | No daily cap or account. Very large files are limited by your device's memory. | Free tiers usually cap tasks per day or file size, with paid plans above that. |
| What can be converted | Some jobs are out of reach in a browser, such as layout-preserving PDF to Word. | Servers can run full desktop engines, which handle some complex documents better. |
Retention windows are each vendor’s own published figure, checked October 2026. For specific tools, see our comparisons of PDF to Word converters, image compressors and HEIC converters.
Developer Verification Guide: How to Verify Zero Uploads
We encourage developers, security researchers, and privacy-conscious users to independently verify our zero-server architecture in any web browser:
The site itself still loads like any other: pages, scripts and, if you accept them, analytics and ads. What never leaves your device is the file you convert.