How to Use This IP CIDR Checker
This free online tool lets you check whether IP addresses fall within one or more CIDR ranges. It's designed for developers, network engineers, and security professionals who need a quick, reliable way to verify IP-to-subnet membership.
Step-by-Step
- Enter CIDR ranges in the left box — one per line (e.g.,
192.168.1.0/24,10.0.0.0/8). - Enter IP addresses in the right box — one per line (e.g.,
10.1.2.3,8.8.8.8). - Click ⚡ Check (or press Ctrl+Enter).
- Results are color-coded: ✅ green = match, ❌ red = no match, ⚠️ yellow = invalid input.
- For each matched IP, the tool shows exactly which CIDR range(s) it belongs to.
Features
- Bulk checking — test hundreds of IPs against hundreds of CIDRs in one click.
- Overlapping CIDRs — if an IP matches multiple ranges, all matching CIDRs are listed.
- Edge case handling — detects invalid IPs, invalid CIDR notation, IPv6 inputs, and leading zeros.
- Zero data collection — everything runs in your browser. Nothing is sent to any server, ever.
- Works offline — after the page loads, you can disconnect and keep using it.
What Is CIDR Notation?
CIDR (Classless Inter-Domain Routing) is a method of representing IP address ranges using a base IP and a prefix length. For example, 192.168.1.0/24 represents all 256 addresses from 192.168.1.0 to 192.168.1.255. The /24 indicates that the first 24 bits identify the network, leaving 8 bits (2⁸ = 256) for host addresses.
Common CIDR Examples
10.0.0.0/8— Class A private network (16.7 million IPs)172.16.0.0/12— Class B private range (1 million IPs)192.168.0.0/16— Class C private range (65,536 IPs)0.0.0.0/0— matches every IPv4 address203.0.113.5/32— matches exactly one IP address
Frequently Asked Questions
What is a CIDR range?
CIDR (Classless Inter-Domain Routing) notation is a compact way to represent an IP address and its associated network mask. For example, 192.168.1.0/24 represents all IP addresses from 192.168.1.0 to 192.168.1.255 — a block of 256 addresses. The number after the slash indicates how many bits of the IP address identify the network.
How do I check if an IP address belongs to a CIDR range?
Enter your CIDR ranges (like 10.0.0.0/8 or 192.168.1.0/24) in the left box and your IP addresses in the right box, one per line. Click Check, and the tool will instantly show you which IPs match which CIDR ranges, with color-coded results for easy reading.
Is my data safe with this tool?
Yes. This tool runs 100% in your browser. No IP addresses or CIDR ranges are ever sent to any server. All processing happens locally on your device using JavaScript. You can even use it offline after the page loads.
Can I check multiple IPs and CIDRs at the same time?
Yes. You can enter as many CIDR ranges and IP addresses as you need, one per line. The tool checks every IP against every CIDR range and shows all matching CIDRs for each IP.
Does this tool support IPv6?
Currently, this tool supports IPv4 addresses only. If you enter an IPv6 address, it will be detected and clearly flagged as unsupported rather than giving incorrect results.
What happens with overlapping CIDR ranges?
If an IP matches multiple CIDR ranges, all matching ranges are displayed. For example, 10.1.2.3 would match both 10.0.0.0/8 and 0.0.0.0/0, and both are shown.
What does /32, /24, /16, /8 mean?
The number after the slash is the prefix length — it tells you how many leading bits define the network. /32 = exactly 1 IP, /24 = 256 IPs, /16 = 65,536 IPs, /8 = 16.7 million IPs. Smaller prefix numbers mean larger networks.