The API Explorer extension can be manually installed and run with a Looker instance using the following steps:

1. create a new LookML project called apix
2. create a new model. In apix.model, put:

   connection: "<any valid connection name>"
3. Use the contents of the linked manifest.lkml as the project's manifest.lkml. The http://localhost:30000 url is for the optional API Explorer file server
4. save all changes and deploy to production
5. in the root of sdk-codegen:

yarn && yarn build && yarn dev:xapix

1. on the Looker web page, click Browse|API Explorer to view the API Explorer