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Every site gets a free FastCat hostname like site-ab34.fastcat.app, live the moment it’s provisioned. When you’re ready, point your own domain at it instead.
A site serves one hostname at a time. While a custom domain is active, your FastCat hostname stays reserved for you but stops serving traffic. Clear the domain field to switch back.

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Add your domain

1

Enter the domain in your panel

Open your site → Security tab → Change domain, type the hostname (example.com or www.example.com), and click Apply. During ordering, the wizard’s domain step does the same thing.
2

Create the DNS record at your registrar

Add the record below wherever your domain’s DNS is managed— Cloudflare, Namecheap, GoDaddy, Hostinger, and so on. The exact IP address to use is shown in your panel next to the instructions.
3

Let us verify it

We check your DNS continuously. The Overview tab moves from Awaiting DNS setup to Issuing SSL certificate, then to Live · SSL active. The page refreshes itself as each step completes.

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The DNS record

@ means “the root of the domain” at most registrars. Cloudflare lets you type the domain itself (example.com) instead.A root— or apex— domain must use an A record. The DNS standard doesn’t allow a CNAME there.
Only the exact hostname you entered serves your site. If you want example.com and www.example.com to work, add a redirect from the other one at your registrar or DNS provider (most offer forwarding rules for free).

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SSL certificates

Once your hostname verifies, Let’s Encrypt issues a certificate automatically— typically 30 to 90 seconds later. Renewals are automatic too; there’s nothing to buy or install.
Don’t visit your domain before the panel says SSL is active. If you load it during the gap, your browser caches its “Not Secure” warning for the whole session, and it will keep showing the wrong certificate even after ours is live. If that happens, close every window for the domain or open a private/incognito window.

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Troubleshooting

Check that the record type is A (not AAAA or TXT), that the value is exactly the IP in your panel, and that there’s no leftover A record for the same host pointing somewhere else. Some registrars keep a default parking record you have to delete.
That’s supported, but the SSL/TLS mode matters— see Cloudflare & proxied domains.
Usually a few minutes. A high TTL on an old record can stretch it to hours, so if you’re planning a cutover, lower the TTL to 300 seconds a day beforehand.
A hostname can only be attached to one FastCat site. If it’s on another of your sites, remove it there first; otherwise contact support.