One question I still have though is what’s the difference between tokenizer.json and tokenizer_config.json - for example if I use RobertaTokenizerFast.from_pretrained() I get the following.

Didn’t find file added_tokens.json. We won’t load it.
Didn’t find file special_tokens_map.json. We won’t load it.
Didn’t find file tokenizer_config.json. We won’t load it.
loading file vocab.json
loading file merges.txt
loading file tokenizer.json

And If I try and load this tokeniser with AutoTokenizer.from_pretrained() it fails since there’s no config.json - I’m trying to train from scratch using the run_mlm.py script.
Is there a step by step guide to training a (custom) tokenizer, then a model (from scratch) using run_mlm.py?