Brave has reached the size where we would like to add brave to the User-Agent string. However, in testing this, we found that many sites don't work correctly with this UA.
We added a JS API to allow sites to detect brave. Unfortunately, this doesn't always work for Brave's partners. Sometimes the ability to detect the UA using a different mechanism is required.
In all cases, the information is the same for all users and therefore, cannot be used to distinguish users.
If Yandex is the default search engine, we add a clid parameter to search requests to indicate that they are coming from Brave. Our clid is assigned by Yandex, so it looks like a random number but is actually the same for all users on a platform. On Android, you would see 2423859 in the URL, and on desktop, you would see 2353835.
It helps the Brave Search backend to understand whether the requesting browser has Brave Rewards enabled. As such, the header X-Brave-Ads-Enabled: 1 is added to navigation requests to Brave Search in non-private windows. Otherwise, the header is not added.