If you have 100 separate JSON files, each with one contact, use a terminal script (macOS/Linux):
In a cramped apartment that smelled faintly of coffee and solder, she balanced a laptop on her knees and a tiny thrift-store speaker on the windowsill. Her latest freelance job was deceptively simple on paper: convert a messy JSON export of contacts from an old CRM into a tidy VCF file a client’s phone could import. The client wanted “one-click” simplicity; the JSON was anything but. json to vcf converter