I copy&pasted a citation I had handy:

259. L. Velho and J. de Miranda Gomes. Digital halftoning with space filling curves. ACM
SIGGRAPH Computer Graphics, 25(4):81–90, 1991.

It sees that as two references, so move it to a single line. (The documentation at the bottom says "please make sure each reference starts on a new line" but I did not know the documentation existed.)

It assigned "25(4):81–90" as "Volume / Issue" (annoying, the text is a "before" CSS that I can't copy&paste).

However, the BibTeX has a different assignment(?!):

@article{velho1991a,
citation-number = {259.},
author = {Velho, L. and Miranda Gomes, J.},
title = {Digital halftoning with space filling curves},
volume = {25},
date = {1991},
pages = {81–90},
language = {en},
journal = {ACM SIGGRAPH Computer Graphics},
number = {4}
}

Note that the "." was incorrectly included in the citation number and the "de" was dropped from the name "J. de Miranda Gomes". It did recognize that the title is in English.

Annoyingly, it is not possible to see that BibTeX without downloading. I would like to see it in the GUI so I could, eg, copy&paste. Also, all downloads have the same name, so I end up with Firefox adding (1), (2), etc. to the filenames.

The documentation says "in case the parser got something wrong just select individual tokens like you would select text in your favourite text editor". It does not seem to have a way to say the tokenization itself was wrong, and I do not know why the graphical tokenization is different than the BibTex one.

I ended up just ignoring the graphical display and only looked at the BibTeX.

I tried a citation to a paper with a French title:

W. Sierpinski. Sur une nouvelle courbe continue qui remplit toute une aire plane. Bulletin de
l’Académie des Sciences de Cracovie, Série A, pages 462–478, 1912

It ended up with:

@article{sierpinski1912a,
author = {Sierpinski, W.},
title = {Sur une nouvelle courbe continue qui remplit toute une aire plane},
pages = {462–478,},
date = {1912},
language = {fr},
journal = {Bulletin de l’Académie des Sciences de Cracovie, Série A}
}

The pages incorrectly includes a comma, it correctly identified the title as French (nice), otherwise it looks fine.

I gave it a trickier one - the paper is in German, published in the same French journal where Sierpinski published:

G. Polya. Über eine Peanosche Kurve. Bulletin de l’Académie des Sciences de Cracovie, Série A, pages 1–9, 1913.

Giving:

@article{polya1913a,
author = {Polya, G.},
title = {Über eine Peanosche Kurve. Bulletin de l’Académie des Sciences de Cracovie},
pages = {1–9,},
date = {1913},
language = {fr},
journal = {Série A}
}

The title is wrong (it includes most of the journal name), the pages contains an extra comma, and the language is wrong.

Lastly I tried a complex entry:

M. Griebel and G. Zumbusch. Hash based adaptive parallel multilevel methods with space-
filling curves. In H. Rollnik and D. Wolf, editors, NIC Symposium 2001, volume 9 of NIC
Series, pages 479–492. Forschungszentrum Jülich, 2002.

giving:

@inproceedings{griebel2002a,
author = {Griebel, M. and Zumbusch, G.},
title = {Hash based adaptive parallel multilevel methods with space-filling curves},
editor = {Rollnik, H. and Wolf, D.},
volume = {9},
pages = {479–492},
date = {2002},
language = {en},
series = {of NIC Series},
booktitle = {NIC Symposium 2001},
address = {Forschungszentrum Jülich}
}

The only tweak is to remove the "to" in the series. (The "official" BibTex for the book at https://juser.fz-juelich.de/record/189313 shows "Forschungszentrum Jülich" is correctly described as the address - I was surprised! I thought it would be the publisher, but that is the "NIC Scientific Council".

Overall, pretty good. I might use it as a first pass rather than my usual solutions of typing everything into Zotero directly, seeing if the publisher has a pre-built reference, or using Google Scholar citation as my starting point.