Whishper uses faster-whisper in the backend.

Simply put, it is a complete UI for Faster-Whisper with extra features like transcription translation, edition, download options, etc…

Whisper models have a very good WER (word error ratio) for languages like Spanish, English, French… if you use the english-only models it also improves. Check out this page on the docs:

https://whishper.net/reference/models/#languages-and-accuracy

No, it’s completely independent, it does not rely on any third-party APIs or anything else. It can function entirely offline once the models have been downloaded.