Watchman is an open source project developed by Facebook. As the name of the software CORRECTLY suggests that it watches files and keep TRACK of changes in files. It can also trigger action based on file change. React native uses watchman to provide hot reloading feature of React Native. Hot reloading of React native application helps the developer to build application faster. 

Native mobile application development doesn’t have this feature which means, a developer has to make changes and compile the project to see an out on the device. But React native saves TIME by AUTOMATING this task and provide hot reloading. With React native, if the developer makes any change in the project file, the watchman will DETECT the change and invoke the build to reflect the changes automatically without any developer intervention. Hot reloading feature of React native make it a developer friendly framework and definitely speed up the development. Installation of the watchman is mentioned in the React native’s environment setup step.ac