y509 is a terminal user interface for inspecting and validating X.509
certificate chains.

Features:
- Interactive TUI for browsing certificate details, extensions and the
  chain hierarchy
- Chain validation against the system trust store, flagging missing
  intermediates, wrong ordering and expired certificates
- Live server inspection over TLS, including STARTTLS for SMTP, IMAP
  and PostgreSQL
- Export certificates to PEM/DER files or copy them to the clipboard
- JSON output for scripting and CI/CD pipelines
- Reads certificates from PEM/DER files, remote servers or stdin