The Crawler by itself is a paid add on. Your application needs access to the Crawler to use it.
The Crawler has a free version you can use with Netlify, or, if relevant to your use cases, Zendesk and DocSearch. If you try to add a new application to that crawler that doesn't have access, you will get an error.
You can also run your own version of DocSearch using the documentation here. However please note this is legacy and no longer supported.