Compare two lists

Good to know

• This is not a diff. Order does not count here: the same lines in a different sequence are the same list. The text comparison tool answers the other question, where moving one line changes everything after it.
• Without "count repeats", a line is either in a list or not, however many times it was pasted. With it, three copies in A against one in B leave two in "only in A" and one in "in both" — which is the answer you want when the lists are stock counts rather than e-mail addresses.
• Ignoring case collapses all four I letters before lowercasing. It has to: the plain lowercase of İSTANBUL is an i followed by a separate dot, which never matches istanbul, and Turkish rules turn ISTANBUL into ıstanbul, which does not match either. ş and ö stay distinct letters, because that is what they are.
• A trailing space is invisible and turns one entry into two different ones, so both boxes are trimmed by default. The lines shown in "in both" are spelled the way A spells them; with "ignore case" on, B may have written them differently.
• Each line is looked up once rather than searched for, so two lists of a hundred thousand entries compare in the time it takes to paste them. Everything happens in your browser — nothing you paste is sent to the server.