How to use the IP Subnet / CIDR Calculator
1. Enter an IP address with CIDR prefix notation (e.g. 10.0.0.0/8, 192.168.1.64/26).
2. Click Calculate — network address, broadcast, usable host range, subnet mask, and host count are shown instantly.
What is it?
CIDR (Classless Inter-Domain Routing) notation combines an IP address with a prefix length (e.g. /24) to define a network block. The prefix specifies how many bits are the network portion — the remaining bits are host addresses.
A /24 subnet has 256 addresses (2^8), with 254 usable hosts (the network address and broadcast address are reserved). Subnetting is fundamental to VPC design, firewall rules, access control lists, and network segmentation.
Benefits
Know exactly who and what is visiting your app
User agent parsing reveals browser name, version, operating system, device type, and whether a request comes from a real user or a bot — essential for analytics, feature flags, and traffic analysis.
Convert curl commands to ready-to-use fetch code
Paste any curl command — from browser DevTools, documentation, or Stack Overflow — and get the equivalent JavaScript fetch API call, ready to drop into your application.
Catch server misconfiguration before users do
Inspect HTTP response headers for missing CORS policies, incorrect Content-Type values, broken cache directives, and absent security headers like CSP and HSTS.
Test API endpoints in the browser without Postman
Send GET, POST, PUT, and DELETE requests with custom headers, bodies, and query parameters directly in your browser — no installation, no account, no context switching.
Frequently asked questions
What is the broadcast address?
The last address in the subnet. Packets sent to the broadcast address are delivered to all hosts in the subnet. It cannot be assigned to a host.
What are /30 and /31 subnets used for?
/30 gives 2 usable hosts — commonly used for point-to-point links between routers. /31 (RFC 3021) gives 2 addresses both usable for point-to-point links, but has no broadcast.