What is the difference between dependencies and dev_dependencies in a pubspec.yaml? It seems that when I run pub get the dev_dependencies aren't downloaded.
dependencies are the dependencies that become part of your executable or library your pub package is providing to others.
dev_dependencies are dependencies that are not available for code in the resulting application, but only for tests, examples, tools or to add executable tools like for code generation to your project.
dev_dependencies do not affect packages that "consume" this package as dependency no matter whether it is a dependency or adev_dependency there.
See also