Capsule

Capsule is a file-sharing tool built around one simple promise. You drop in a file, you get back a short link and a QR code, and the file is gone in an hour. There are no accounts, no sign-up, and no inbox full of share notifications, just a link you hand to someone before it quietly expires. It sits somewhere between a pastebin and a full file host, close to the ease of a temporary link but with real encryption underneath the moment you ask for it. For anyone who has emailed a file to themselves just to move it between machines, or spun up a whole cloud bucket for a single one-time transfer, it's the lighter option that does one job and then forgets about it.

The workflow is deliberately bare. The web app has a send mode and a receive mode, and to send you drag and drop a file, paste it, or click to browse, after which Capsule uploads it and hands back a link plus a scannable code. File IDs read as three little words, something like duck-view-time, so they're easy to say out loud or type on another device, and to receive you just enter that phrase on the receive screen. Keyboard shortcuts cover the common actions so you can move without reaching for the mouse, and the interface follows a light, dark, or system theme so it fits wherever you open it.

The limits are the point rather than an afterthought. Uploads cap at 100 MB per file with a 2 GB per hour ceiling, and everything is deleted automatically after sixty minutes with no backups, so recovery is impossible once the window closes. That makes Capsule a bad choice for anything you need to keep and a good one for a quick handoff you'd rather not leave sitting on someone's server forever. The short lifetime is a feature, not a compromise, because nothing lingers to be indexed, leaked, or dug up later. If a transfer matters for the next few minutes and not the next few years, that expiry is doing exactly what you want.

What sets it apart is optional end-to-end encryption that runs entirely in your browser. Flip the encrypt toggle before sending and the file is scrambled on your device before anything leaves it, so the server only ever stores the ciphertext and a boolean flag noting the file is encrypted. It never sees your key or your plaintext, which is what makes this a genuinely zero-knowledge design rather than a promise about how the operator behaves. In exchange you're handed a recovery phrase you have to save, because without it the file genuinely cannot be recovered, and that's the honest cost of holding the only key yourself.

The encryption is standard rather than homegrown, which is the reassuring part. Capsule uses the age v1 format with a scrypt passphrase recipient and ChaCha20-Poly1305 authenticated encryption, and the key material is a 12-word BIP39 mnemonic generated locally from 128 bits of entropy. Because it's plain age ciphertext with no proprietary wrapper, a file encrypted in the browser can be decrypted by the command-line tool and the other way around, so you're not locked into one client or one vendor's format. Beyond the encrypted bytes the server keeps only the filename and size, nothing more, so there's little there to expose even before you factor in the encryption. Even if someone got hold of the storage, there's no key sitting next to the data to find, and encryption stays opt-in so the plain flow keeps moving fast for files you don't care about.

Capsule isn't only a web page. You can upload straight from the terminal with a one-line curl command against its upload endpoint, install a proper CLI on macOS, Linux, or Windows through a short install script, or use the Android app, and package managers are supported too. That suits developers who want to move a file off a server or out of a script without opening a browser at all, and the same short links and browser-grade encryption work across every client, so a file dropped from curl can be pulled back down in a browser and a phrase read off one screen types cleanly into another. It's the same small tool wearing whatever interface the moment calls for.

Being open source under AGPL-3.0 is more than a license badge here. The source for the server and the Android client is public on GitHub under the withcapsule organization, so you can read exactly what happens to a file, confirm that encryption really runs before upload, and check the retention behavior for yourself rather than taking it on faith. The hosted service, made by Sean Singh, is free with no account, and if you'd rather not trust a shared instance you can self-host your own on infrastructure you control, keeping even the ciphertext off a stranger's server. If you need long-lived links, huge files, or team management, that narrow focus is the tradeoff, but for quick, disappearing, optionally encrypted transfers it does exactly what it says.