Management at a former employer quite rightly freaked out when they realised that their devs on a certain subcontinent were routinely pasting their code into external web-based prettifiers to format it nicely...
1. JSON prettifying
2. JWT decoding/verification (bonus for "paste your signing key and we will generate JWTs for you too!")
3. PEM <-> DER conversion
I'd love to see "standard" prettifiers for HTML, CSS, JSON, YAML, and TOML. The required libraries exist and the problem isn't terribly hard if you aren't picky about corner cases. I'm sure countless programmers have written such tools already. Where is the disconnect?
There's a CLI linter for pretty much every language I've used, but how would you prettify a valid YAML file? Any reformatting will change it semantically.
(1): Which can be necessary to prevent accidental problems like NO defaulting to false not "NO" and similar. I personally strongly recommend against anything where string quotes are optional for human written/edited serialization formats (and comments are a must have).