Documentation of the Bukkit API can be found at hub.spigotmc.org/javadocs/bukkit/. The Bukkit.jar file that you built in Chapter 1, Deploying a Spigot Server also contains the Spigot API, which can be found at hub.spigotmc.org/javadocs/spigot/. The Spigot API is a superset of the Bukkit API, which means that it contains all the classes, interfaces, and so on that are present in the Bukkit API, as well as some additional classes that are unique to the Spigot project. If you want your plugin to support Spigot and CraftBukkit servers, then you will want to develop by using the Bukkit API. If you choose to only support Spigot servers, then you can develop using the Spigot API. In this book, we will refer to the Bukkit API. However, using the Spigot API will yield the same results.