A particular tag can be viewed like this: https://musicbrainz.org/tag/filk/ but to see all the tags, you need to go to https://musicbrainz.org/tags and what's worse, if you do simply remove the last part of the URL, giving https://musicbrainz.org/tag – it just reports 404. It would be more intuitive, at least to me, if it redirected to the list of all tags.