NetPad

Subnet, CIDR, IP and timezone tools in your toolbar. Every answer is worked out on your own machine.

Add to Chrome

The point
IT and security staff are told not to paste internal data into unknown web tools — yet subnet ranges, hostnames, tokens and log timestamps are exactly that. Every online alternative is somebody else's server. NetPad makes no network requests at all.

What it does

Subnet and IP Network and broadcast addresses, first and last usable host, host counts, wildcard masks, prefix and netmask conversion. Point-to-point /31 links and single-host /32 handled properly. Private, public, reserved and multicast ranges identified. Test whether an address sits inside a network, either way round.
Time A live timezone board of the cities you actually work with, as a split-flap departure board. Epoch conversion both ways, in seconds, milliseconds, microseconds or nanoseconds, with the unit read from the number. Meeting overlap across zones. Daylight saving handled, including the hour that does not exist when the clocks jump forward.
Encoding Base64 in both alphabets, URL encoding, JSON validation and pretty-printing with errors by line and column, and JWT decoding with the timestamp claims shown as real times. The signature is not verified — that would need the issuer's key, and a network request.
Right-click anything Highlight a line of a firewall log, right-click, and NetPad picks the addresses and the timestamp out of it. It reads only text you deliberately select: Chrome hands it over directly, so the extension needs no access to any page.

Permissions

Two, and no more: contextMenus and storage. No host permissions, no activeTab, no content scripts. NetPad cannot read the pages you visit, and the manifest blocks outbound connections at the browser level rather than merely promising not to make any.

Deploying it across a team? There is a page for IT administrators with the extension ID, the policy snippets for allowlisting, and how to verify all of the above yourself.

Price

Free. No account, no upsell, nothing collected.