Install Gatesites
Chrome, Edge, Brave, Opera, Vivaldi, or anything else built on Chromium version 108 or newer. Roughly a minute.
Download
One zip file. Unpack it somewhere you will not delete by accident, because Chrome loads the extension from that folder every time it starts.
Put it in the browser
Unpack the zip
Somewhere permanent. Your documents folder is fine. The downloads folder is a bad idea, because clearing it later would remove the extension.
Open the extensions page
Paste chrome://extensions into the address bar. In Edge it is edge://extensions, in Brave brave://extensions.
Turn on developer mode
The switch is in the top right corner. It has to stay on, because Gatesites is not in the Chrome Web Store yet and this is how Chrome loads an extension from a folder.
Load unpacked
Click Load unpacked and choose the folder you unpacked. Pick the folder that directly contains manifest.json, not the zip and not a folder above it.
Pin it
Click the puzzle piece in the toolbar and pin Gatesites. The settings page opens by itself the first time.
Chrome shows a "Disable developer mode extensions" prompt at startup while developer mode is on. Dismissing it leaves Gatesites running. Clicking disable turns it off, so choose carefully, and check the toolbar icon is still there after a restart.
Set it up in the right order
Add your rules first
Open the settings page and build the block list, switch on the categories you want and set any schedules. Do this before the password exists, so you are not unlocking your way through your own setup.
Then hand it over
Go to the Password section and choose Hand it over. Give the keyboard to the other person. They set the password, choose how strict it should be, and print or write down the recovery code.
If they are not in the room, share your screen and let them type. Do not have them read it out to you.
Test it once
Visit a blocked site. You should see the block page, and pressing "Open it anyway" should start the countdown rather than opening anything. If it does, you are done.
Updating and removing
To update, download the newer zip, unpack it over the same folder, and press the reload arrow on the Gatesites card in the extensions page. Your rules, statistics and password survive an update.
To remove it, use Remove on the same card. That deletes everything Gatesites stored, including the rules and the password. There is no way to prevent this, and the overview page is honest about why.
Locking it down properly
On a machine you administer for someone else, Chrome's own enterprise policy can force-install an extension so that it cannot be removed from the extensions page at all. That is a Chrome feature rather than a Gatesites one, and it is the only arrangement that genuinely survives a determined afternoon.
Pair it with filtering at the router or through a DNS provider. A browser extension protects one browser. Anything that matters should not depend on a single layer.
There is also a stricter route that does not involve Gatesites at all. Chrome, Edge and Brave read a pair of Windows policies, URLBlocklist and URLAllowlist, from the registry. Setting the first to * and the second to the handful of sites you need shuts the browser to everything else, across every profile and incognito window, with no extension involved and no way to remove it without administrator rights. Ask if you want the script for it.