How to convert files without uploading them

Most online file converters upload your files to their servers. OnlyFiles is different. Every conversion runs directly in your browser using pure JavaScript — your files never leave your device. This means complete privacy, instant processing, zero server storage, and the ability to convert even when offline.

Why browser-based conversion matters

Uploading sensitive documents to a server introduces risk. Your file could be intercepted, logged, or stored longer than you expect. Browser-based conversion eliminates that risk. Since all code runs on your computer in your browser tab, your data never touches a server. The processing is also instant — no waiting for files to upload, no waiting for server processing, no waiting for downloads. And because your browser does all the work, conversion even works offline. Simply load the page while online, then disconnect and keep converting.

Which OnlyFiles tools run in the browser

OnlyFiles is built on browser-based conversion. All of these run entirely on your device, with zero uploads:

• Image conversions: JPG ↔ PNG, JPG ↔ WebP, PNG ↔ WebP, GIF, BMP, TIFF, and more
• iPhone photo format: HEIC to JPG
• PDF conversions: PDF to JPG, PDF to PNG, JPG/PNG to PDF
• Spreadsheet conversions: CSV to Excel, Excel to CSV
• PDF tools: Merge PDF, split PDF

How it works technically

OnlyFiles uses well-established JavaScript libraries that run entirely in your browser. Image conversions use HTML5 Canvas, a standard browser feature for image processing. PDF operations use pdf.js for reading, jsPDF for writing, and pdf-lib for advanced manipulation like splitting and merging. Spreadsheet operations use SheetJS for Excel and CSV parsing. All of these libraries are open-source and run 100% in JavaScript inside your browser tab. Your file enters your browser, gets processed by JavaScript running on your computer, and exits as a download — the server never sees it.

How to verify no upload happens

You can verify this yourself. Test 1: Disconnect internet. Load any OnlyFiles conversion page while online. Disconnect from WiFi or ethernet. Try converting a file. It works perfectly, proving no server call is being made. Test 2: Check the network tab. Open your browser's developer tools (F12), go to the Network tab, and convert a file. You'll see zero network requests to OnlyFiles servers — only requests to load the initial page. This proves the conversion happens entirely in your browser.

Why this matters for privacy

If you're converting a tax return, medical document, passport photo, bank statement, or any other sensitive file, uploading it to a server means trusting that server with your private information. Browser-based conversion removes that trust requirement. Your file stays on your device. No server logs it, stores it, or accesses it. You get speed, privacy, and the peace of mind that comes with knowing your sensitive data never left your computer.

Getting started

Pick any conversion tool from OnlyFiles. For example, if you want to convert an image from JPG to PNG, visit /convert/jpg-to-png. Drag your file in, click convert, and download. The entire process happens on your device, no uploads, no servers, just instant results.

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