Hi transliterators,
I am still supporting Skrutable, so feel free to ask me for improvements.
For doing large amounts of text, there are two bugs I know about, and here are the workarounds (I hope to eventually fix them):
1. Don't attempt too much in the UI input box. After about 2–3 thousand characters (depends on the input scheme), it will fail. Instead, use the "whole-file upload" button after choosing settings.
2. For "whole-file upload", if the filename has diacritics (e.g. "tēst.txt" or "तेस्त.txt"), it will fail. Eliminate these and it should work. If you're starting with IAST, one quick way to do this is to use Skrutable's "IASTreduced" scheme (e.g., "śāntarakṣita_vādanyāyaṭīkā" becomes "santaraksita_vadanyayatika").
Also, don't forget about
https://www.aksharamukha.com/converter, which not only does whole files, too, but also just works great and supports lots of scripts/schemes. It seems to also struggle with #1 above, but #2 is not a problem.