Yes, you can absolutely buy a domain from any registrar (Namecheap, Cloudflare, GoDaddy, etc.) and use it with your Railway service. You would add it as a custom domain in your service's networking settings, then configure the CNAME and TXT records at your registrar as shown in the dashboard. Buying through Railway at railway.com/domains gives you auto-configured DNS with no manual record setup, included WHOIS privacy, and auto-renewal, while buying externally gives you more control over DNS and the flexibility to move your domain independently, but requires you to manually set up the required DNS records.

does that mean that if i buy domain through railways, I will have to use it within railways only, and I won't be able to use it externally in future ?