Matrix

What it is

Matrix is an open network for secure, decentralised communication, and the project’s own shorthand is the clearest description of it: Matrix works like email, but for instant messaging. Nobody owns email; you choose a provider, and your address is tied to it. Matrix works the same way. Accounts live on a homeserver, which is bound to a single domain that cannot change over time, and a Matrix ID combines a username with that domain — @username:example.com.

The decentralisation is not decorative. Homeservers communicate with each other using a Server-Server API, so a room can contain people whose accounts are on entirely different servers, and messages are relayed between those servers rather than stored in one company’s cloud. Clients only ever talk to the homeserver of the account they are using, through the Client-Server API.

History you can check

The federation model raises an obvious question — how do participants agree on what happened — and Matrix answers it with signatures. When a server accepts a message it adds it to its own graph of history, linking it to the most recent unlinked objects, and then signs the event together with the signatures of its parent objects to produce a tamper-resistant signature for the history. The server relays the signed event over HTTPS to the other servers in the room, which validate the signature, validate the request’s authentication signature against identity spoofing, and check whether the sender’s historical permissions allowed that message. If the checks pass, the event joins their history too.

Where servers briefly disagree — two people replying at the same moment — Matrix is built to tolerate it: each server keeps its own view, later messages link to both branches, and the histories converge. The project describes this as eventual consistency and integrity of the distributed room history.

Bridges, the specification, and who maintains it

Bridges connect Matrix to platforms that are not Matrix — the project names IRC, Discord and Slack — by creating users that mimic the other side. Those mirrors are called ghosts on the Matrix side and puppets on the third-party side, and bridges can be limited to a namespace to reduce the risk of abuse. Application services are the mechanism: unlike a bot, which has to be invited into every room, an appservice can monitor every unencrypted event within its namespace.

The specification itself is open and versioned, browsable at spec.matrix.org, and published under the Apache-2.0 licence. Governance is public: anyone can propose an amendment through a Matrix Spec Change, which is discussed openly and, once the author believes the concerns are addressed, enters a formal review by the Spec Core Team. The current release is v1.19. The standard is stewarded by the Matrix.org Foundation, funded by memberships and donations rather than by licensing, and the surrounding ecosystem — homeservers, clients, SDKs and bridges — is built by many different parties rather than one company.

What it costs, and what it asks of you

There is nothing to buy. Matrix is a protocol and the specification is free to read and implement, so the cost of using it is whatever your chosen homeserver and client charge — and many are free.

What it asks in exchange is a decision most messengers make for you. There is no single app to install; you install a client and register on a homeserver, and the domain of that homeserver becomes part of your identity permanently. That is the point of the design, and it is also the reason Matrix is not the right choice for someone who simply wants a chat app that works.