Yes — readthedocs.io has IPv6.

Has both IPv4 (A) and IPv6 (AAAA) addresses.

IPv6 readiness

Website, mail and DNS all work over IPv6.

Website over IPv6 readthedocs.io has 2 IPv6 addresses and answers on every one we tested. ✓ 2606:4700::6810:fe78 answers · 443✓ 2606:4700::6810:fd78 answers · 443	yes
www over IPv6 www.readthedocs.io has 2 IPv6 addresses and answers on every one we tested. ✓ 2606:4700::6810:fe78 answers · 443✓ 2606:4700::6810:fd78 answers · 443	yes
Mail servers (MX) have IPv6 Every mail server has an AAAA record. aspmx.l.google.com ✓aspmx2.googlemail.com ✓aspmx3.googlemail.com ✓alt1.aspmx.l.google.com ✓alt2.aspmx.l.google.com ✓	yes
Nameservers have IPv6 2 of 2 nameservers checked have an AAAA record, so IPv6-only resolvers can look the domain up. ivan.ns.cloudflare.com ✓tegan.ns.cloudflare.com ✓	yes

HTTPS over IPv6 · not part of the grade yet
Loads over IPv6 with a valid certificate after 3 redirects: HTTP 200.

https://readthedocs.io/ via 2606:4700::6810:fe78 → 302https://readthedocs.org/ via 2606:4700::6812:61d → 302https://app.readthedocs.org/welcome/ via 2606:4700::6812:71d → 302https://about.readthedocs.com/?ref=app.readthedocs.org via 2606:4700::6810:fe78 → 200

works

Nothing keeping you from an A

Nothing to fix
Show it off: add the badge to your README.
[![IPv6](https://aaaa.bot/badge/readthedocs.io.svg)](https://aaaa.bot/readthedocs.io)

Check again

readthedocs.io Has IPv6

A (IPv4)	104.16.253.120 104.16.254.120
AAAA (IPv6)	2606:4700::6810:fe78 2606:4700::6810:fd78

www.readthedocs.io Has IPv6

A (IPv4)	104.16.253.120 104.16.254.120
AAAA (IPv6)	2606:4700::6810:fe78 2606:4700::6810:fd78

Browsers on dual-stack networks will usually pick IPv6 here (the "Happy Eyeballs" algorithm races both and prefers v6).

Copy the evidence — a citation-ready record of this measurement

IPv6 measurement: readthedocs.io
Measured 2026-10-31 05:04:33 UTC by aaaa.bot (one server on Fly.io, region iad)

A (IPv4):    104.16.253.120, 104.16.254.120
AAAA (IPv6): 2606:4700::6810:fe78, 2606:4700::6810:fd78
www AAAA:    2606:4700::6810:fe78, 2606:4700::6810:fd78

Readiness grade A: Website, mail and DNS all work over IPv6.
- Website over IPv6: readthedocs.io has 2 IPv6 addresses and answers on every one we tested.
    2606:4700::6810:fe78: answers (TCP 443)
    2606:4700::6810:fd78: answers (TCP 443)
- www over IPv6: www.readthedocs.io has 2 IPv6 addresses and answers on every one we tested.
    2606:4700::6810:fe78: answers (TCP 443)
    2606:4700::6810:fd78: answers (TCP 443)
- Mail servers (MX) have IPv6: Every mail server has an AAAA record.
- Nameservers have IPv6: 2 of 2 nameservers checked have an AAAA record, so IPv6-only resolvers can look the domain up.

Reachability = a TCP connection opened on port 443 (or 80).

HTTPS over IPv6 (not graded): Loads over IPv6 with a valid certificate after 3 redirects: HTTP 200.
    https://readthedocs.io/ via 2606:4700::6810:fe78 -> HTTP 302, certificate: valid
    https://readthedocs.org/ via 2606:4700::6812:61d -> HTTP 302, certificate: valid
    https://app.readthedocs.org/welcome/ via 2606:4700::6812:71d -> HTTP 302, certificate: valid
    https://about.readthedocs.com/?ref=app.readthedocs.org via 2606:4700::6810:fe78 -> HTTP 200, certificate: valid
DNS answers via DNS-over-HTTPS (Cloudflare). Method: https://aaaa.bot/method
Permanent link: https://aaaa.bot/r/NToOrj6mmK

Permanent link: aaaa.bot/r/NToOrj6mmK · How we measure

Checked 2026-10-31 05:04:33 UTC — one of the top 1,000 sites, re-checked weekly. Re-check now. Full DNS report: dns.pizza/domain/readthedocs.io · JSON: /api/v1/readthedocs.io