Netscape once created a file format for storing cookies on disk so that they would survive browser restarts. curl adopted that file format to allow sharing the cookies with browsers, only to soon watch the browsers move away from that format. Modern browsers no longer use it, while curl still does.
The Netscape cookie file format stores one cookie per physical line in the file with a bunch of associated meta data, each field separated with TAB. That file is called the cookiejar in curl terminology.
When libcurl saves a cookiejar, it creates a file header of its own in which there is a URL mention that links to the web version of this document.
The cookie file format is text based and stores one cookie per line. Lines that start with # are treated as comments.
Each line that specifies a single cookie consists of seven text fields separated with TAB characters (ASCII octet 9). A valid line must end with a newline character.
Fields in the file
Field number, what type and example data and the meaning of it:
string example.com - the domain name
boolean FALSE - include subdomains
string /foobar/ - path
boolean TRUE - send/receive over HTTPS only
number 1462299217 - expires at - seconds since Jan 1st 1970, or 0