caddy

example.org {
        # Set this path to your site's directory.
        root * /var/www/example.org/html

        # Enable the static file server.
        file_server
        # or with file listing enabled:
        # file_server browse
}

@html {
  path_regexp html ^/(.*)\.html$
}
redir @html /{re.html.1} 301
try_files {path}.html