What Matter Actually Standardises
Matter gets described as the standard that makes smart home devices work together. That is roughly true, and the detail of what it does and does not cover decides whether a product built on it behaves the way buyers expect.
Ask three people what Matter is and you'll get three answers: a radio protocol, a cloud service, and a logo on a box. None of those is right, and the gap between them is where product teams get into trouble.
Matter is an application-layer standard. It defines a data model and the messages that move across it: a device describes itself as a set of endpoints, each endpoint holds clusters, each cluster has attributes and commands. A dimmable light has an On/Off cluster and a Level Control cluster, and any Matter controller knows what those mean without being told anything specific about the manufacturer. That is the whole trick, and it's worth being precise about it, because what Matter standardises is the vocabulary rather than the behaviour underneath.
It also standardises commissioning, security and the trust model. A device joins a fabric by presenting a certificate chain that traces back to an attestation authority, which is why a Matter device can be added to a home without the installer trusting the vendor's cloud. Multi-admin is part of the specification too: the same physical device can belong to several fabrics at once, so a light can be controlled by two different ecosystems without either one acting as a gateway for the other.
What Matter does not standardise is the transport in any single sense. It runs over Thread, over Wi-Fi and over Ethernet, and the specification deliberately leaves the choice to the device. That flexibility is also the main source of field confusion, because a Thread device needs a border router and a Wi-Fi device does not, and nothing on the retail box explains the difference to the person buying it.
It also does not standardise features your product sells on. If a device does something no cluster describes — a specific wash cycle, an unusual sensor fusion, a scheduling behaviour — that capability either maps awkwardly onto existing clusters or lives outside Matter in the vendor's own app. Device types are added with each specification release, and the list grows, but it will always trail what manufacturers want to ship.
Nor does it make your cloud unnecessary. Matter gives you local control, which is a genuine improvement on a product that stops working when a data centre has a bad afternoon. Firmware updates, analytics, account linking and anything involving a user on a different continent still run through your own infrastructure.
There is one more thing worth saying to anyone specifying a Matter product: certification tests interoperability, not quality. A certified device has demonstrated that it speaks the protocol correctly against a test harness. It has not demonstrated that its radio performs in a house with foil-backed insulation, that its battery lasts as long as the datasheet claims, or that the vendor will still be issuing firmware in four years. Those remain your problem, and they are the ones customers will actually complain about.