Import passwords, in Vault's sidebar, reads a CSV export from Generic CSV, Google/Chrome Password Manager, Bitwarden, or 1Password. The file is parsed entirely in your browser and never uploaded to Magpie - only the items you review and confirm are encrypted and saved, the same way a manually entered item is.
Rows that look like something already in your Vault (matching domain and username, or a matching title) are flagged as possible duplicates and left unchecked, with a one-click option to skip all of them.