Ask DNS if it is DNS

dig +short _isitdns.isitdns.net TXT

"v=isit1 surface=8 round=180 spec=https://isitdns.net/wiki/tools/ask-dns"

dig +short isit.isitdns.net A

stamp          = 4DIGIT "-" 2DIGIT "-" 2DIGIT "T" 2DIGIT ":" 2DIGIT ":" 2DIGIT "Z"
day            = 4DIGIT "-" 2DIGIT "-" 2DIGIT
as-of          = "as of " stamp
count          = "0" / %x31-39 *DIGIT
word           = "no" / "mostly" / "maybe" / "no data"
help-1         = "is it DNS? " verdict " isitdns monitors common public DNS providers. " [ count " no data, " ] as-of
verdict        = "no."
                 / "mostly. " count " of " count " resolvers are struggling."
                 / "maybe. " count " of " count " resolvers are down."
                 / "no data. " nd-reason "."
                 / "no data yet. " yet-reason "."
nd-reason      = "fewer than two networks have reported; the last reading is " age " old"
                 / "the probe readings could not be read"
                 / "the board round's reading is stamped in the future; no verdict until the clocks agree"
                 / "no database is bound; nothing was read"
yet-reason     = "no probe has reported"
reason         = nd-reason / yet-reason
age            = count "m" / count "h " count "m" / count "d"
help-2         = "ask: isit why ksk cloudflare google quad9 adguard, all .isitdns.net TXT; A ladder 127.0.0.2 no, .3 mostly, .4 maybe, .5 no data; 127.0.0.1 is never ours; tokens, one string in isit and here: state (ok, degraded, failing, stale), bad, measured, probes, asof; concatenate the strings of a line, no separator"
help-3         = "receipt: https://isitdns.net; probe: ours not yours, your path: https://isitdns.net/wiki/troubleshooting/test-your-own-path"
help-4         = tokens
tokens         = "state=" state " bad=" count " measured=" count " probes=" count " seats=" count " asof=" stamp
state          = "ok" / "degraded" / "failing" / "stale"
version        = "v=isit1 surface=" count " round=" count " spec=" spec-url
spec-url       = "https://isitdns.net/" 1*( %x61-7A / DIGIT / "-" / "." / "_" / "~" / "/" )
version-record = "v=isit1" *( SP vtag )
vtag           = vkey "=" vval
vkey           = 1*( %x61-7A / DIGIT )
vval           = 1*%x21-7E
token-line     = token *( SP token )
token          = tkey "=" tval
tkey           = 1*%x61-7A
tval           = 1*%x21-7E
isit           = isit-1 isit-2
isit-1         = tokens
isit-2         = word
ladder-code    = "127.0.0.2" / "127.0.0.3" / "127.0.0.4" / "127.0.0.5"
why            = not-fine ", " as-of
                 / "all measured resolvers answering, " as-of
                 / "no data: " reason ", " as-of
not-fine       = rstate *( ", " rstate )
rstate         = board-id " " ( "slow" / "partial" / "bad" )
board-id       = ldh-label
ldh-label      = alnum [ *38( alnum / "-" ) alnum ]
alnum          = %x61-7A / DIGIT
resolver       = status *( SP leg )
resolver-id    = "cloudflare" / "google" / "quad9" / "adguard"
status         = resolver-id " " rstatus " " latency [ ", " note ] ", " dnssec ", " as-of
                 / resolver-id " no data, " as-of
rstatus        = "ok" / "slow" / "partial" / "bad"
note           = "failing from " dlist "; slow from " dlist / "failing from " dlist / "slow from " dlist
dlist          = dname *( ", " dname )
latency        = count " ms" [ " from " dname ] / "unreachable" / "n/a"
dname          = probe-name / domain-id
probe-name     = "the" 1*%x61-7A
domain-id      = 1*%x61-7A
dnssec         = "dnssec validating" / "dnssec not validating" / "dnssec unknown"
leg            = family " " transport " " leg-latency " " leg-state
family         = "v4" / "v6"
transport      = "doh" / "dot" / "tcp53" / "udp53"
leg-latency    = count "ms" / "--"
leg-state      = "ok" [ SP rcode ]
                 / ( "unreachable" / "failing" ) [ " from " probe-list ]
probe-list     = probe-name [ *( ", " probe-name ) " and " probe-name ]
rcode          = 1*%x41-5A
ksk            = keys "; roll " day "; of " count " public resolvers via sentinel: " count " trust " tag ", "
                 count " do not yet, " count " no sentinel support, " count " not validating, "
                 count " no determination (both SERVFAIL), " count " unreadable; " as-of
keys           = "root KSKs published: " tag *( ", " tag ) / "root KSKs: unread"
tag            = 1*5DIGIT

dig +short isit.isitdns.net TXT | python3 -c '
import calendar, math, re, sys, time
a = sys.stdin.read()
p = re.findall(r"(\w+)=([^\s\"]+)", a)
t = dict(p)
for k in ("state", "asof"):
    if k not in t: sys.exit("not fine: no %s token in the answer" % k)
if len(t) != len(p): sys.exit("not fine: a token key appears twice")
w = {"no": "ok", "mostly": "degraded", "maybe": "failing", "no data": "stale"}
if w.get((re.findall(r"\"([^\"]*)\"", a) or [""])[-1]) != t["state"]: sys.exit("not fine: word and state disagree")
if not re.fullmatch(r"\d{4}-\d\d-\d\d[Tt]([01]\d|2[0-3]):[0-5]\d:([0-5]\d|60)[Zz]", t["asof"]): sys.exit("not fine: asof is not a valid stamp")
try: age = math.floor(time.time() - calendar.timegm(time.strptime(t["asof"].upper(), "%Y-%m-%dT%H:%M:%SZ")))
except ValueError: sys.exit("not fine: asof is not a valid stamp")
ok = t["state"] == "ok" and -180 <= age < 600
print("fine, %ds old" % age if ok else "not fine: state=%s, %ds old" % (t["state"], age))'