Free proxies make money somehow, and with most of them it is advertising: banners on the landing page, pop-ups inside the sites you visit, and ad networks setting their own cookies along the way. Some also keep a record of your IP address and the pages you open for weeks. Shifter Web Proxy shows no ads at all, because the business behind it is selling proxies, not attention.
We do not log the pages you visit. To enforce the free allowance, the service keeps one anonymous counter per browser: a random identifier, stored only as a hash, with the time and data you have used today. It does not record your IP address, and it is not linked to a name or an account, because there is no account.
For HTTPS websites, the encrypted connection is set up inside your browser tab, so our gateway relays traffic it cannot read. The gateway does need the name of the site you are connecting to, as every proxy does, and it does not write it to a log.
The quick check before each session is Google reCAPTCHA, which follows Google's privacy policy. It keeps bots from using up the network that real visitors share.
One sensible rule applies to any proxy, ours included: do not enter passwords or card details on a site you do not trust. Read more in Are residential proxies legal?