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CIDR range calculator
A range as the fewest blocks, blocks joined, and the overlap of two sets.
It runs entirely in this browser tab: the addresses, names and passwords you type are never uploaded, and the tool makes no network request while it works. Open your browser's network panel and try it — nothing leaves the page.
Settings
- What to show
- The blocks that cover the range, the range each block covers, or a count of both. Choices: The fewest blocks, Each block's range, Count them.
- The other set
- Blocks or ranges, one a line, to compare the input against.
- Compare
- What to do with the other set: nothing, the addresses in both, or the ones only in the first. Choices: Nothing, What both hold, What only the first holds.
How to use it
- Paste your text into the box above, or open a file.
- Adjust the settings beside it until the result is what you wanted.
- Copy the result, or save it as a file. The result updates as you type.
Questions
- Does this look anything up?
- No, and that is the point of the group. Nothing here resolves a name, queries a registry or opens a connection. Three tools would want a table bigger than the whole application — the vendor prefixes, the routing table, the full port register — and each of them takes the table from you and says so rather than answering "unknown" about something that exists.
- Why does the subnet calculator show the bits?
- Because a prefix stops being a mystery the moment you see it written out. It is also where the two lengths everybody gets wrong become obvious: a /31 is a point-to-point link with two usable addresses and no broadcast, and a /32 is one host rather than minus one.
- Can I paste something confidential in?
- Yes, and that is why the group is built this way. An internal addressing plan, a DKIM private key's public half, a Wi-Fi password and an authorisation header are all things you would think twice about typing into a website. None of them is sent anywhere, and the request builder hides credentials by default so that what you paste into a ticket is safe to.
- Is what I type uploaded anywhere?
- No. This page carries the whole tool as WebAssembly and runs it on your own device. You can watch your browser's network panel while you use one.
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