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🌐 CIDR Subnet Calculator

Parse a single IPv4 CIDR locally in your browser and compute the normalized subnet, mask, wildcard mask, network, broadcast, and usable endpoint range.

V1 is a local `IPv4 CIDR` calculator only. The input must be a single `A.B.C.D/P` value such as `192.168.1.10/24`. The tool normalizes the address into its subnet explicitly and handles `/31` and `/32` with dedicated rules. It does not auto-fix input, support IPv6, or provide network-planning advice.

Only a single `A.B.C.D/P` input is accepted. Plain IPs, dotted masks, IP ranges, URLs, hostnames, and IPv6 are rejected. Editing the input after success or error invalidates the previous result immediately.

Status Initializing
Normalized CIDR —
Prefix Length —
Total Addresses 0
Usable Endpoints 0
Input Role —
Diagnostics 0
Input IPv4 —
Normalized CIDR —
Prefix Length —
Subnet Mask —
Wildcard Mask —
Network Address —
Broadcast Address —
First Usable —
Last Usable —
Total Addresses —
Usable Endpoints —
Host Bits —
Input Address Role — 
Initializing the interactive runtime. Please wait.

Scope boundary: this version only supports a single `IPv4 CIDR`. It does not support `IPv6`, CIDR summarization, subnet splitting, IP range to CIDR conversion, private/reserved address classification, DNS/ASN/WHOIS lookups, or any network access.

Rule note: regular prefixes follow common network / broadcast / usable host rules; `/31` is treated as a point-to-point special case under `RFC 3021`; `/32` is treated as a single-address host route.

Privacy note: parsing, calculation, and copy actions stay local in the current browser. Avoid pasting real production ranges, internal office networks, or sensitive network-planning data.

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Free online CIDR subnet calculator. Parse a single IPv4 CIDR locally in your browser and compute the normalized subnet, mask, wildcard mask, network, broadcast, and usable host range. V1 supports IPv4 CIDR only and does not do IPv6, route summarization, network advice, or network lookups.