The html5 emulator for Varvara encodes roms in the url so they can be easily shared. The encoding is twofold:

a) A running length compression pass, so series of bytes that look the same are combined:
https://wiki.xxiivv.com/site/ulz_format

b) A base64 encoding so the binary data can be represented with readable characters:
https://wiki.xxiivv.com/site/base64.html

Both schemes have been implemented in uxn natively:

ulzenc: https://git.sr.ht/~rabbits/uxn-utils/tree/main/item/cli/base64/b64enc.tal
b64enc: https://git.sr.ht/~rabbits/uxn-utils/tree/main/item/cli/lz/ulzenc.tal