You pay for the connection. Everything past it should belong to everyone.

A network for sharing things, with nobody in the middle

Send someone a file. Put a website online. Both work without an account, without paying anyone, and without asking permission, and they keep working when the Internet does not.

Underneath, one idea does the work: a server should be able to hold your data without being able to read it, and the thing that unlocks it should never travel the same road. Files are encrypted in your browser; the key rides in the part of a link that browsers never send to a server.

Encryption stopped being the hard part

Every mainstream file service encrypts in transit and at rest. What none of them do is give up the ability to read the file, and that ability is what gets subpoenaed, breached, scanned and monetised. The interesting question is not "is it encrypted" but who holds the key.

The same is true of publishing. A domain is rented, a certificate is issued, and a host serves the bytes: three parties, each of whom can be leaned on to make a page disappear or say something else. A .capsule name has none of them, because the name and the signing key are the same object.

The key goes around the relay

A capsule is a file split into chunks, each encrypted with AES-256-GCM under a key generated in the browser. The nonce is a random prefix plus the chunk index, and the associated data binds every chunk to the protocol version, so a downgrade fails to authenticate rather than silently succeeding.

A name nobody issues, a page nobody can rewrite

capsule site publish ./www packs a folder into one capsule, stores it on relays, and signs a short record saying which capsule is the current version of your name. Relays hand that record out and gossip it to each other. They cannot forge one, they have no key, and they cannot quietly serve an old one, because every record carries a sequence number the browser remembers.

The extension does something ordinary browsers do not: it rebuilds every page before showing it. Stylesheets, images and fonts from the bundle become data: URLs; anything pointing at the open web is removed; a link that leaves CAPSULE becomes a click you have to confirm. The result lands in a sandboxed frame with connect-src 'none' and no scripts.

A .capsule site cannot make a single network request. Not a font, not a pixel, not a beacon. That is a property of the format, not a setting you can forget to turn on.

Every hop knows one step, and no hop knows two

Encryption hides what you sent. It does not hide that you sent it, to whom, or when. With --mix, a request is wrapped in a Sphinx packet, one layer per hop, every packet exactly 65,920 bytes, and each relay peels one layer, waits a random time, and forwards. The reply comes back along a second path the destination cannot see, into a mailbox you poll.

None of that matters if there are four nodes and one operator. So the CLI prints how much protection the live network actually offers before every mixed send, in those words, and the design document leads with the same caveat rather than burying it.

Where CAPSULE sits among the alternatives

Two tables. The first is what CAPSULE was built to do differently. The second is every other system on the map, with the limitation it is known for and whether CAPSULE answers it, often only partly.

✓ by design and tested  ·  ~ partly  ·  WIP designed, not built  · , not addressed.
This table is about the design. What the network is today is smaller, and therefore weaker, than the design allows: the threat model says exactly where.

Everything else on the map, and what it says it cannot do

Each of these solves a real problem well. The limitation quoted is the one that system is known for; the last column is whether CAPSULE addresses it, and the answer is often "partly" or "no".

Four commands to join the network

To join the public network instead of running alone, point your relay at a peer with CAPSULE_PEERS and set CAPSULE_PUBLIC_URL. Gossip does the rest.

One line, and something else does the reading

If you use Claude Code, Codex or anything like them, each of these is a single line to paste. The first one is first on purpose: you are about to run code from a stranger on the internet, and an agent is good at telling you what it does before it does it.

The last clause of each is the point. An agent that reports what a relay observes, or what a build script touches, is more useful than one that just finishes.

Boring choices, on purpose

Nothing here is novel cryptography. Every primitive is one that has been looked at for years by people better at this than we are; the work is in the composition, and the composition is the part that has not been audited.