Guides
Handle apex domains and subdomains
Respect adapter capabilities without guessing public-suffix boundaries.
Domain SDK validates full hostnames but does not guess registrable apex domains with a two-label rule. Use domains.capabilities.apexDomains for provider support.
Railway apex instructions use ALIAS/ANAME or CNAME flattening. Vercel supports apex configuration. Cloudflare for SaaS exposes CNAME routing and reports apex support unavailable. Render accepts wildcard domains; other current adapters reject them.
For tenant hostnames under a domain you own, use createSubdomainClient to constrain direct-child labels and choose wildcard or individual provisioning.
Read next: Provider overview.