Yeah, using rune in benchmarks drops 230.1 ns/op to 139.2 ns/op for yodositiiiiuyildogdsxsqsosssoqdsvesooos on my machine, significantly faster. You avoid string conversion, since it allocates a new string every time it converts a rune to a string.

you can use fmt.Sprintf insted of "+" to make your code even cleaner :)

take a look at strings.Builder :)

show better fail messages not only "true" or "false"

error detail should be more clear