About Kilnfile
Kilnfile is a free collection of 47 file tools built and run by Uthman Choudhury, an independent developer in the UK. Every tool processes files inside your browser using open-source libraries, so nothing is uploaded. The site is funded by display advertising and has no accounts, limits or watermarks.
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Who runs Kilnfile?
Kilnfile is written and maintained by Uthman Choudhury. The site started from a simple frustration: most online converters make you upload private documents to a server, then cap you at a few files a day. Modern browsers can do the work themselves, so Kilnfile does it that way. There is no company behind the site, no investors, and no plan to add accounts.
How do the tools work?
When you open a tool, your browser downloads the code for that one job (for example a PDF library or FFmpeg compiled to WebAssembly) and runs it in a Web Worker on your device. The file you choose is read from your disk into memory, transformed, and offered back as a download. At no point does the file travel over the network. You can confirm this by opening your browser’s developer tools, watching the Network tab, and running a conversion: you will see the library load, but never an upload.
Because the work happens on your device, speed depends on your hardware. Video jobs on an older phone can take a few minutes.
Which libraries and data sources does Kilnfile use?
| Component | Used for | Licence |
|---|---|---|
| pdf-lib (Cantoo fork) | Merge, split, rotate, reorder, page numbers, password protect and unlock | MIT |
| PDF.js (Mozilla) | Render PDF pages to images and extract text | Apache 2.0 |
| FFmpeg (ffmpeg.wasm) | All video and audio conversion, trimming, compression and GIF export | LGPL 2.1 / MIT wrapper |
| libheif via heic-to | Decode iPhone HEIC and HEIF photos | LGPL 3.0 / MIT wrapper |
| mammoth | Read Word .docx files for Word to PDF; PDF to Word writes .docx with a small built-in OOXML writer | BSD 2-Clause |
| UPNG.js | Lossy PNG colour quantisation for PNG compression | MIT |
| JSZip | Bundle batch results into a single zip download | MIT |
| Browser Canvas, WebCodecs and Web Workers | Image resizing, cropping and format conversion, all off the main thread | Built into the browser |
Source: package manifests in the Kilnfile repository, checked 20 September 2026.
How are the guides researched?
Every guide states its data source at the bottom of the page. Figures such as file size limits, bitrates and format capabilities come from the official documentation of the software or service concerned (for example WhatsApp’s help centre or the PDF 2.0 specification) and are re-checked when the guide’s last-updated date changes. Where a number comes from our own testing, the guide says so and describes the test. Facts are kept consistent across pages: if a limit changes, every page that mentions it is updated together.
How is the site funded?
Kilnfile shows display adverts through Google AdSense. Adverts load only after a tool is ready to use and only after you have made a cookie choice, and they never see your files. There are no affiliate links in the tools or guides.
How can I get in touch?
Found a bug, a wrong fact, or want a tool that is missing? Email hello@kilnfile.com. Corrections are usually applied within a few days and the page’s last-updated date is bumped. See also the privacy and cookies page.