Contact
Get in touch.
One address, read by a person. Corrections to the maths are the most welcome kind of mail — a single reproducible case is worth more than a long description.
Written in English. No newsletter, no mailing list — an address sent here is used to reply and nothing else, as set out in the privacy policy.
What to write about
A number looks wrong
The most useful thing anyone can send. Include the exact input, what the page showed, and what you expected instead.
A tool is missing
Say what you were trying to work out and where you gave up. Concrete tasks make better tools than feature names.
Something is unreadable
Broken layout, unusable with a keyboard, poor contrast in either theme — with your browser and screen size if you can.
Privacy or legal
Questions about the privacy policy or terms, and any takedown or attribution request, go to the same address.
Reporting an incorrect calculation
Every figure on the site comes out of one arithmetic module with its own test suite, so a genuine error is usually reproducible from a single input. The fastest report contains four things:
- The exact input, copied rather than retyped —
10.0.4.0/22, not "a /22". - Which page and which field.
- The value shown.
- The value you expected, and briefly why.
That is enough to turn the report into a failing test. Where the disagreement is about a convention rather than a bug — whether a /31 has usable hosts, for instance — a pointer to the relevant RFC settles it quickest.
What cannot be answered here
The site makes no network requests and keeps no records, so questions that need either cannot be answered: who holds an address, where a device is, why a service blocked you, or what traffic crossed a network. Those belong with the operator of the network concerned, or with the regional internet registry that allocated the block.
Requests to remove, alter or disclose data about a visitor cannot be acted on either, for the plain reason that no such data exists to remove — the privacy policy explains exactly what is and is not stored.
Contact questions
Is there a contact form?
No. A form needs a server to receive it, and this site does not have one — it is a set of static files with no backend and no database. Email is the only channel, which also means nothing you send passes through a third-party form service first.
How quickly will I get a reply?
This is a small project run alongside other work, so allow several days. Reports of an incorrect calculation are read first, because they affect everyone using the tool.
Can you tell me who owns an IP address, or where it is located?
No. The calculator performs arithmetic on the address you type and makes no network requests, so there is no lookup capability here — no WHOIS, no geolocation, no reverse DNS. A regional internet registry WHOIS service is the right place for ownership questions.
Can you help with an abuse report or a blocked address?
No. This site is unrelated to any network you may be reporting or blocked by, and holds no logs that could identify anyone. Abuse reports belong with the network operator responsible for the address, which WHOIS will name.