The refractiveindex.info database is a comprehensive, open-source repository of optical constants for a wide range of materials, compiled from peer-reviewed publications, manufacturer datasheets, and authoritative texts. The database uses a YAML-based format to ensure data integrity, consistency, and ease of access. Each data record includes detailed metadata, enabling users to understand and utilize the data effectively. The complex index of refraction, $ \tilde{n} = n + ik $, is essential for understanding optical properties, with n representing refraction and k representing absorption. The database includes both linear optical constants (n and k) and nonlinear optical constants (n₂), which describe the refractive index's variation with optical field intensity. The data is systematically organized, with each record containing references to the source publication, data values, and optional metadata. The database is continuously updated and maintained, with a focus on accuracy and reliability. Users can access the data through a user-friendly interface, including an interactive data browser and a hierarchical catalog structure. The dataset is available at Figshare and is freely accessible under the Creative Commons Zero (CC0) license, allowing unrestricted use, distribution, and modification. The database serves as a valuable resource for researchers, engineers, and students in optics and photonics, providing a reliable and comprehensive collection of optical constants for various materials.The refractiveindex.info database is a comprehensive, open-source repository of optical constants for a wide range of materials, compiled from peer-reviewed publications, manufacturer datasheets, and authoritative texts. The database uses a YAML-based format to ensure data integrity, consistency, and ease of access. Each data record includes detailed metadata, enabling users to understand and utilize the data effectively. The complex index of refraction, $ \tilde{n} = n + ik $, is essential for understanding optical properties, with n representing refraction and k representing absorption. The database includes both linear optical constants (n and k) and nonlinear optical constants (n₂), which describe the refractive index's variation with optical field intensity. The data is systematically organized, with each record containing references to the source publication, data values, and optional metadata. The database is continuously updated and maintained, with a focus on accuracy and reliability. Users can access the data through a user-friendly interface, including an interactive data browser and a hierarchical catalog structure. The dataset is available at Figshare and is freely accessible under the Creative Commons Zero (CC0) license, allowing unrestricted use, distribution, and modification. The database serves as a valuable resource for researchers, engineers, and students in optics and photonics, providing a reliable and comprehensive collection of optical constants for various materials.