What is torznab?

Torznab is a standard API specification used to access and query various torrent indexers and trackers on the internet. It was developed as a part of the Sonarr project, which is an open-source software application used to manage and automate TV show downloads. Torznab provides a common set of requests and responses that can be used by different applications to interact with various torrent indexers and trackers, easing the implementation of new automation tools. It includes support for the search functionality of several popular torrent indexers such as Jackett, RARBG, and others. Torznab makes it possible for users to search and download torrents across multiple trackers and indexers, which is especially useful for users looking for files that might not be available on a single tracker.