Do Not Track
Do Not Track (DNT) is a browser setting from 2009 that added a DNT: 1 header asking websites not to track the user; it was never legally binding, most sites ignored it, and browsers have been removing it in favor of Global Privacy Control.DNT started in 2009 as a proposal from privacy researchers and was adopted by Firefox in 2011, then by every major browser. A user who switched it on had the header DNT: 1 sent with each request. The W3C's Tracking Protection Working Group tried for years to agree on what a site had to do when it received the header, and closed in January 2019 without a standard that the industry accepted. Because no law required compliance, advertising networks and most websites simply ignored it, and California's CalOPPA only required sites to say in their privacy policy whether they honored it.
Browsers have since retired it. Mozilla removed the setting from Firefox in version 135 (February 2025), explaining that few websites respected it and that it could be used as a fingerprinting attribute, and pointed users to the "Tell websites not to sell or share my data" setting that sends Global Privacy Control instead. Apple had dropped DNT from Safari in 2019 for the same fingerprinting reason.
The difference between the two signals is legal, not technical. GPC carries the same kind of one-bit message, but California, Colorado, Connecticut and a growing list of US states require businesses to treat it as a valid opt-out of the sale and sharing of personal data, so ignoring it is a violation. A consent tool therefore reads GPC and can safely ignore a DNT header that a few older browsers still send.