"key functionality" is correct and usable in written English.
It is used to describe an important or essential feature of something. For example: "The new software update provides improved key functionality for managing customer accounts."
The IT underpinning the Department for Work and Pensions' (DWP) Work Programme was not fully functional when the scheme was launched and some of its key functionality is still not available, according to a National Audit Office NAOO) report.
The key functionality of the Synergizer application programming interface (API) is represented here by the function translate (line 11).
Social networking, for example, is a key functionality.
Design specifications were written and prototypes made of key functionality.
The circuit board provides some key functionality to the project.
Consumers are using low-quality substitutes that lack key functionality or don't stand up to challenging environmental conditions.
Specifically, we propose a complete design of NAPS, including its key functionalities, system flows, interfaces, and individual module design.
The site has been designed to be easy to navigate, yet has still retained the key functionalities of the main website, with members being able to log in using their existing profile and log-in details".
In addition, a prototype testbed is also introduced, and the proof-of-concept demonstrations of OpenScale's key functionalities in both data plane and control plane are conducted.
This integration enables the realization of many of the key functionalities for optical networking to be realized in a manner appropriate to real deployment.
To achieve intelligence in the future grid, a highly accurate state estimation is necessary as it is a prerequisite for many key functionalities in the successful operation of the power grid.
