IPv4 CIDR Checker
Paste a CIDR range and one or more IPv4 addresses to see which of them belong to the range.
- Runs in your browser
- Free to use
About this tool
Whether a given address is covered by a firewall rule, an allow list or a provider's prefix is a question that comes up constantly, and getting it wrong by hand is easy. The IPv4 CIDR Checker does the bit-level comparison for a whole list at once and returns a clear inside / outside verdict per address with counts, all computed locally in the browser.
Use it to validate ACL entries, to confirm that a reported IP really belongs to the range you were told, or together with the IP extractor to classify addresses pulled from a log file.
How to use it — quick steps
- 01
Enter the cidr range
Type or paste the cidr range in the field above, for example 10.0.0.0/8. Nothing is uploaded.
- 02
Press "Check addresses"
Press "Check addresses" or Ctrl + Enter. The result appears instantly below the form.
- 03
Read the result
It appears in the dark panel under the form instantly. Every block has [copy] and other actions.
Key features of this tool
Nothing leaves your browser
The processing is plain JavaScript that runs on your device: the text you paste is never uploaded to our servers or to anyone else.
Instant results
Results appear the moment you press the button, even for long inputs, and every block has copy and download actions.
Works everywhere
No installation, no account and no limits: the tool works on desktop and mobile, in any modern browser, as often as you like.
Frequently asked questions
How is membership decided?
The address and the network are converted to 32-bit integers and masked with the prefix length; if the masked values match, the address is inside the block.
Can I check thousands of addresses?
Yes, the check is instant even for large lists. Invalid lines are flagged rather than silently skipped.
Does it support IPv6?
This tool is IPv4 only. Use the IPv6 CIDR Calculator to obtain the first and last address of a v6 block and compare manually.