Swagger inspector is not an open source tool. Also swagger-core only works with Maven/Gradle. It would have been great if there was a dedicated Java class that can scan for annotations and generate swagger document without depending on Maven/Gradle.
Also, swagger-codegen is an open-source and it supports many programming languages. In the same way, swagger-scanner would be a wrapper would generate swagger docs and it would support multiple programming languages. Also, it would not depend on a specific build tool.
Many of the open-sourced swagger projects do not have good document. A document should clearly lay out input, output and procedure to get output.