Over the past few decades, a vast amount of information on the structure of atomic nuclei has been collected, compiled, and evaluated. Accurate and reliable data are essential for the understanding of the behavior of atomic nuclei. Accessing and utilizing these data, spread among different databases, has remained challenging for many researchers due to the complexity and diversity of data formats. This article presents the Toolkit for Nuclei (TkN) C++ open-source library that provides easy access to nuclear structure data. This library is intended to be used in theoretical models, data analysis software or simulation codes. It utilizes a comprehensive database built from different official sources and frequently updated. The user interface allows to easily access and search for nuclear structure data and TkN can be compiled without any dependencies, facilitating its incorporation into various research projects.