# IPv6 Readiness Explorer

> Is a domain reachable over IPv6? Web, DNS and mail checks, address classes and a scored report. Checks AAAA records for a domain and its www host, IPv6 addresses of its name servers and mail servers, classifies every IPv6 address (global unicast vs ULA, link-local, documentation, 6to4, Teredo, NAT64 …), optionally opens a TCP connection to port 443 over IPv6, and turns it into a score with every check explained.

Part of usefulweb.site (https://usefulweb.site/). Results are deterministic calculations from the inputs and the listed assumptions; the API returns exactly what the web page shows.

## Use it
- Human interface: https://ipv6readinessexplorer.usefulweb.site/ (interactive tool at https://ipv6readinessexplorer.usefulweb.site/tool)
- JSON API: POST https://ipv6readinessexplorer.usefulweb.site/api/v1/calculate with a JSON object of inputs (schema: https://ipv6readinessexplorer.usefulweb.site/api/v1/tool)
- OpenAPI: https://ipv6readinessexplorer.usefulweb.site/openapi.json
- MCP (Streamable HTTP): https://ipv6readinessexplorer.usefulweb.site/mcp - tool `ipv6_readiness_explorer`

## Inputs
- mode (select): Mode
- domain (text): Domain
- connectTest (boolean): Also try a TCP connection to port 443 over IPv6 from this server
- pasted (textarea): Record set (JSON) - Pasted mode: {domain, hosts:[{name, ipv4, ipv6}], nameservers:[…], mx:[{name, priority, ipv4, ipv6}], connect?:[{host, address, ok, code}]}

## Method
- Resolves A and AAAA for the domain and www.<domain>, the NS host names and the MX host names (up to 10) with this server's resolver.
- Every IPv6 address is classified against the IANA IPv6 special-purpose registry: only global unicast (2000::/3 minus special blocks) is reachable from the internet.
- Score (points, n/a checks are excluded from the maximum): apex AAAA 25, www AAAA 15, any name server with IPv6 20, all name servers with IPv6 10, MX with IPv6 15 (pro rata), no special-purpose addresses 5, TCP 443 over IPv6 10. Grade A ≥ 90, B ≥ 75, C ≥ 50, D ≥ 25.
- Connect test: up to 3 global AAAA addresses of the domain/www, TCP handshake on port 443 with a 5 s timeout. If this server itself has no IPv6 route (ENETUNREACH/EADDRNOTAVAIL), the test is reported as not possible instead of counted as a failure.