increment.dnsp.co
A counter that must rise on every request.
What it does
Each request moves the answer up by one, expressed as an address, until it wraps back around at 255.255.255.255. Because no two answers repeat, a repeat is proof that you read a stored copy rather than a live one.
Example
$ dig @dnsp.co increment.dnsp.co +short
0.0.14.72
$ dig @dnsp.co increment.dnsp.co +short
0.0.14.73
Reading the answer
a higher value each time
You are reaching us live on every query.
the same value twice
A cache between you and us answered the second one.
values jumping by a lot
Other people are querying too. Only the direction matters, not the step size.
Notes
- Run it three or four times in a row. One pair is not much evidence.