Convertle is a free file converter I built that runs entirely in the browser. You drop in an image, video, audio file or document, pick an output format, and the conversion happens on your own device. Nothing is uploaded to a server.
That choice changes more about hosting than about the interface. A converter that never receives your files needs no upload endpoint and no job queue. This post covers what Convertle does, how it works, and what it takes to deploy a site built this way.
What Convertle does
The site converts images, video, audio and documents and lists more than 100 formats. It is free and needs no account.
On the image side it handles the common formats (HEIC, JPG, PNG, WebP, AVIF, SVG) and a long specialist list that includes camera RAW files such as CR2, CR3, NEF, ARW and DNG, plus PSD, TIFF, ICO, EXR and DDS. Video covers MP4, WebM, MKV and MOV. Audio covers MP3, WAV, FLAC, OGG and AAC. For documents it supports DOCX, Markdown, HTML and EPUB. Input and output support varies by format, and what you can use depends on your browser and settings.
The home page has quick presets for the conversions people ask for most: HEIC to JPG, WebP to PNG, MP4 to MP3, Word to Markdown and MKV to MP4. You can convert one file or a whole folder, choose the output formats and download the results together. The defaults work as they are, and you can tune quality, size and codecs if you want more control.
How it works
Convertle runs on WebAssembly plus the media APIs built into the browser, and all of it happens client side. The conversion engines download when you first need them and are then cached in the browser, so the first load needs an internet connection.
Your original files are never changed. The converted output downloads to your device. For large video files, some conversions use temporary browser storage, which is cleaned up when you remove the conversion from the list.
{/* ADD (optional): which engines or libraries run the conversions. Only name them if you have confirmed them. */}
What having no backend does to hosting
A conventional converter has to receive the file, run the conversion on server CPU, hold the result somewhere and delete it later. Each step costs money and leaves something to monitor: upload bandwidth, compute time, storage, cleanup jobs, and abuse handling for anyone who finds the endpoint.
With client-side conversion the visitor's device does the work. Your host serves the page and the engine files, and that is the whole job. Cost follows how many people load the site, not how many files they convert, and a burst of conversions never touches your server.
{/* ADD (optional): where Convertle is hosted (provider and plan) and what it costs per month. */}
The tradeoff is that the visitor's hardware sets the ceiling. A phone and a gaming PC will not convert the same long video at the same speed, and you cannot add capacity by upgrading a plan.
Privacy comes from the architecture
Convertle's privacy page says file contents are never uploaded. The architecture is what makes that promise cheap to keep. There is no upload endpoint to secure and no stored file that could leak.
You can check this yourself. Open your browser's network tab during a conversion. The engine downloads will show up, but a request carrying your file should not.
The policy, updated on October 25, 2026, covers the rest. Theme and settings preferences are kept in localStorage. The hosting provider sees normal web requests, such as IP address and browser information, but never file contents. Analytics are disabled in this deployment.
Deploying a WebAssembly-heavy Next.js site
Convertle is built with Next.js and TypeScript. If you are deploying something similar, a few hosting details are worth checking early. These are general points, not a description of Convertle's own setup.
Serve .wasm files with the application/wasm MIME type so browsers can compile them while they download. Give engine files versioned filenames and long cache lifetimes, since they are large and meant to be cached. Turn on Brotli or gzip compression for them. Some multithreaded WebAssembly builds also need cross-origin isolation headers (COOP and COEP). Check whether your engine does, because those headers can break embedded third-party scripts and iframes.
Plan for the first visit as well. A new visitor pays the engine download once, and later visits read it from the cache.
{/* ADD (optional): one real thing that was hard to build, plus any numbers you measured (load time, a sample conversion time, the device you tested on). */}
The limits
Convertle has no paid size cap. The real limits are device memory, browser limits and the engine doing the conversion. Large videos can be slow or fail, and some formats depend on browser codec support. The fix the site suggests is to try another output format or a smaller file. I would rather the page say that plainly than hide it.
Frequently asked questions
Is Convertle free?
Yes. There is no account and no paid size cap.
Are my files uploaded anywhere?
No. Conversion runs in your browser and file contents are never uploaded. The hosting provider sees ordinary web requests, such as IP address and browser details, but not your files.
Why did my large video fail to convert?
Large videos are limited by your device's memory, your browser and the engine. Try another output format or a smaller file.
Which formats does Convertle support?
More than 100, across images, video, audio and documents. Support for a given input and output pair depends on the format, your browser and your settings.
Convertle is at convertle.help.
