Two acronyms get used almost interchangeably in EV charging, and they should not be. A CSMS and a CPO describe different things: one is a piece of software, the other is a company. Confusing them is common enough that a lot of buying decisions get muddled by it, so it is worth being precise about what each one is.
What a CSMS actually is
CSMS stands for Charging Station Management System, sometimes written CPMS (Charge Point Management System) in older material; the terms mean the same thing, and CSMS is the name the OCPP standard itself uses for a network's backend. It is software, not a company or a service. A CSMS is the platform that a charger connects to over OCPP: it authorises charging sessions, monitors chargers in real time, applies smart charging and load-balancing rules, handles billing and invoicing, and reports on usage across a fleet of charge points.
Put simply, the CSMS is the brain behind the wall-mounted or floor-standing box. The charger itself just delivers power and speaks the protocol; the CSMS decides who gets to charge, at what rate, under what conditions, and hands back the data to prove it.
What a CPO actually is
CPO stands for Charge Point Operator: the company that installs, owns, and runs the charging infrastructure. A CPO's job covers the full lifecycle of a charging site: choosing and procuring hardware, arranging installation and the grid connection, keeping stations maintained and online, billing drivers, and optimising the network over time.
A CPO is a business role, not a piece of technology. It can be a utility running public fast chargers, a retailer offering charging at its car parks, a fleet operator managing its own depot, or a company that exists purely to run charging networks for others.
How the two fit together
A CPO needs a CSMS to run its network; it is the software layer every CPO operation depends on. The relationship is straightforward: the CPO is the operator, the CSMS is the tool it operates with. What is not straightforward, and where most of the confusion comes from, is that a CPO does not have to build or own its CSMS.
Some CPOs run their own, purpose-built platform. Many more license or subscribe to a CSMS from a separate vendor, the same way a retailer might run its own logistics or outsource it to a specialist. Either way, the CPO stays the CPO. Swapping the software underneath does not change who owns the chargers, who bills the driver, or who is responsible when a station goes down.
There is a third role worth naming here too: an EMSP (e-mobility service provider) is the party that gives a driver access to charge, often across many different CPOs' networks through roaming agreements. A single company can hold more than one of these roles at once, which is part of why the terminology gets muddy in practice. But CSMS, CPO and EMSP describe three different jobs, not three names for the same thing.
Why the distinction is worth keeping straight
The practical reason to separate these terms is that they answer different questions. "Who runs this charging network" is a CPO question. "What software manages it" is a CSMS question. And because a CPO's identity does not depend on which CSMS sits underneath it, a CPO's choice of software is not a permanent decision, even though it is often treated as one.
That matters because a CSMS choice made early tends to get locked in by default, not by design. Chargers typically hold one OCPP connection to one backend, so once a fleet is commissioned against a CSMS, changing it means reconfiguring every charger. That is exactly the problem an OCPP proxy exists to solve: it lets a CPO route its OCPP traffic to a new CSMS, or run more than one at once, without touching the hardware.
The free CSMS option
Plugchoice is a CSMS: the core platform, charger management, monitoring, cards and transactions, is free for every OCPP charger connected, with public pricing on the optional modules (smart charging, billing) beyond it. For a CPO evaluating its software layer, that removes the usual first barrier, a sales call and a custom quote, before you can even see what the platform does. Paired with the OCPP proxy, it also means the choice of CSMS stops being a one-way door: a CPO can run Plugchoice alongside an existing platform, or move fully, without a hardware project either way.
