How it works
The converter comes to your file
What actually runs
These are the engines behind the converters — real libraries doing real work, not a wrapper around someone else's API.
Video and audio
FFmpeg (WebAssembly)
The same FFmpeg that powers most video tooling, compiled to WebAssembly and served from this site. It handles transcoding, trimming, merging, frame extraction and GIF creation. It is 32 MB, so it is only fetched the first time you convert media — never on the homepage.
pdf.js and pdf-lib
pdf.js renders and reads pages; pdf-lib writes them. Together they cover merging, splitting, rotating, watermarking, page numbering, text extraction and rendering pages to images — all without a server.
Images
Canvas, libheif and libavif
Most image work uses the browser's own codecs through OffscreenCanvas. HEIC needs libheif and AVIF encoding needs libavif, both as WebAssembly. TIFF, BMP, ICO and GIF encoders are implemented directly against their file formats.
Documents, spreadsheets and archives
SheetJS, mammoth and JSZip
SheetJS parses and writes real workbooks with typed cells. mammoth reads DOCX into semantic HTML. JSZip and fflate handle ZIP, TAR and gzip, with guards against decompression bombs and path traversal.
OCR
Tesseract
Optical character recognition running locally in a worker. The language model is downloaded once and cached by your browser, so scans of sensitive documents never leave your device.
Everything text-shaped
A shared document model
TXT, Markdown, HTML, DOCX, ODT, RTF, PDF and EPUB are all parsed into one internal document structure, and all seven output formats are written from it. That is how one engine produces fifty-plus document conversions — and why a fix to list handling improves all of them at once.
Why this design
Running conversions in the browser is more work to build than shelling out to a server. It is worth it for three reasons.
Privacy stops being a promise. There is no upload, so there is no retention policy to trust, no breach to worry about, and nothing to delete afterwards. You can verify it by disconnecting from the internet mid-session.
It is often faster. A 40 MB video does not need to travel to a server and back. For anything up to a few hundred megabytes, a modern laptop beats the round trip.
It scales without cost. A thousand people converting simultaneously costs nothing extra, because each conversion runs on their own machine. That is what makes the free tier sustainable rather than a loss leader.
Where the approach runs out
Browsers have real limits, and FileTools360 names them rather than papering over them. WebAssembly is 32-bit, so memory tops out around 2 GB — multi-gigabyte video will not work. Legacy binary formats such as .doc and .ppt are undocumented and need LibreOffice to read reliably, which cannot run in a tab. DRM-protected e-books cannot be converted at all, and FileTools360 will not attempt it.
Those conversions are listed in the directory as unsupported, each with the specific reason and a suggested alternative, so you find out before choosing a file rather than after.
Loading only what you need
Every processor is loaded on demand. Opening the homepage downloads none of the conversion engines. Converting a CSV loads the spreadsheet parser and nothing else. Only when you convert a video is the FFmpeg core fetched — and it is then kept warm for 90 seconds in case you convert another, after which its memory is released.
Built from one registry
All 521 converters, plus their pages, metadata, structured data, search index and internal links, are generated from a single conversion registry spanning 11 categories. Adding a converter means adding an entry, not building a page.
FAQ