Hosted Subdomains and Custom Domains

Hosted Subdomains

Hosted CTFd instances are automatically provisioned with a subdomain chosen by the creator. For example: [domain] Instances will be available by default on their hosted subdomain.

All hosted CTFd instances can use a custom domain (e.g. Setup instructions for custom domains are available below.

Because of infrastructure requirements, hosted subdomains cannot be disabled or changed. In addition, subdomains cannot be reserved for any users without having an instance active.

Setting up a Custom Domain

Hosted CTFd instances support the setting of a custom domain which your instance will be accessible at including the subdomain chosen during the creation of the instance.

If you wish to have your instance at the root or apex domain (that is, at instead of, you may need to switch DNS providers to a DNS provider that supports CNAME Flattening, ALIAS records, or ANAME records first.

To set this custom domain use the following instructions:

  1. Go to to see all hosted CTFd instances you have deployed
  2. Select your chosen instance and click the blue gear icon on the right.


  1. Follow the instructions provided to set your custom domain to a CNAME of your * subdomain. You will need to set the custom domain CNAME setting at your domain’s DNS provider. The custom domain will not be set until the CNAME setting is properly configured and active.

    If you are using Cloudflare as your DNS provider you should not enable the Cloudflare proxy (e.g. the orange cloud). Cloudflare proxying can cause hosted CTFd systems to have difficulties in provisioning SSL certificates and identifying user IP addresses.


  2. Once your domain is set, you can still access your CTFd instance through the * subdomain. To remove or change your domain please contact us.