I have been telling people to use https://metadata.nostr.com/ to recover lost follow lists, but when I tried to use it I learned it isn't very good for that, so I wrote https://follows.nostr.com/, which focuses on just that one thing and hopefully does it well enough.
Discussion
This only deals with contacts, not tags.
But patches for that are accepted at nostr:naddr1qqrkvmmvd3hhwucpz3mhxue69uhhyetvv9ujumn0wd68ytnzvupzqwlsccluhy6xxsr6l9a9uhhxf75g85g8a709tprjcn4e42h053vaqvzqqqrhny4gexp5