Console

php craft placard/preview 123                    # an entry's card
php craft placard/preview --title="Hello world"  # a dummy card

Also takes --label, --description, --meta and --image. Output goes to storage/runtime/og-images-preview/.

Cards render the first time they're asked for, and are cached after that. Crawlers like Facebook's and LinkedIn's give up on slow images, so saving an entry also renders its card in a queue job (see renderOnSave). Bulk resaves (resave/entries) skip this, as do config changes, which change every card. To render those in one go:

php craft placard/generate                          # every entry's card
php craft placard/generate --section=news --site=en # comma-separate several handles

Also takes --type. Cards already cached are skipped, as are entries that share an image of their own.