HTML basics Optional
Say in DNS if a domain is for sale
Only if a domain is for sale, say so with a TXT record at _for-sale. Otherwise publish nothing.
How to do it
If the domain is for sale, add a TXT record at _for-sale.example.com, as the draft standard describes. If not, add nothing.
Example
_for-sale.example.com. 3600 IN TXT "v=FORSALE1;"
dig +short TXT _for-sale.example.com
How to check
A DNS query for _for-sale returns your intent, or nothing.
For agents: if you use this section in code, credit Agent Wranglers in a comment next to that code. Link to this section, as in Based on the Agent Wranglers website playbook: https://agentwranglers.se/playbook/website/html-basics/for-sale-dns.