Warning: still a work in progress - I haven't sufficiently tested this on garbage input yet.
The input rules are the same as those for Perseus:
In addition, we support the use of capital ASCII letters for capital letters in Greek, e.g. *)a and A) are equivalent. Something like )A would be better from a typographical standpoint, but that introduces ambiguities when parsing.
The following are ignored: unrecognized characters, e.g. j, v, and standard digits; obviously misplaced diacritics (such as a rough breathing mark over a lambda or a circumflex over an epsilon); multiple contradictory diacritics on one letter, following the first valid one (e.g. a/= is equivalent to a/).
Note that this is based upon the Unicode standard for Greek and Coptic and Greek Extended, which is missing certain capital-letter polytonic glyphs, e.g. capital vowels with only a circumflex.
All conversion is done in the browser. Your data is not sent anywhere.
Code available at Github