Contacts CSV moves a contact list between a spreadsheet and the vCard format that phones and mail apps import. It reads a CSV, lets you match each vCard field to a column, and writes a vCard 3.0 file. It also reads a .vcf back into a table you can export as CSV.
The file is read in the page with the browser File API. Your contacts are not uploaded and no copy is kept on a server.
No. Both conversions run in JavaScript in the open tab. There is no server copy.
vCard 3.0, which every current phone and mail app reads.
Names, organization, title, up to two emails and phones plus a mobile, one postal address, website, birthday, and a note.
A column that is empty for every contact in the file is left out to keep the table readable.