Cidr Calc

Calculate subnet information from CIDR notation. Use when the user asks to calculate a subnet, find the network address, broadcast address, host range, subne...

Security Scan

The skill is an instruction-only CIDR/subnet calculator whose requirements and instructions are consistent with its stated purpose; no credentials, installs, or broad access are requested.

Purpose & Capability

Name and description match the SKILL.md instructions: the skill only describes validating CIDR input and computing subnet parameters. It does not request unrelated binaries, environment variables, or installs.

Instruction Scope

Instructions stay within the expected scope (validation, subnet math, class and private/public determination, binary output). One minor correctness issue: the SKILL.md lists 127.x.x.x as Private — 127.0.0.0/8 is loopback/host-local, not a private RFC1918 network. Also check edge cases (0.0.0.0, 255.255.255.255, /31 and /32 semantics) if you rely on this for production use.

Install Mechanism

No install spec and no code files — instruction-only skill. Nothing will be written to disk or downloaded during install.

Credentials

Requires no environment variables, credentials, or config paths — the declared requirements are minimal and appropriate for a local calculation utility.

Persistence & Privilege

always is false and the skill does not request persistent or elevated platform privileges. Autonomous invocation is allowed by default but not combined with any sensitive access.

Assessment

This appears safe and coherent for computing subnet details. You can install it without exposing credentials or installing extra software. Before relying on it for critical tasks, test its outputs on edge cases (e.g., 0.0.0.0, 255.255.255.255, /31, /32) and note the documented mistake treating 127.x.x.x as a private network (it is loopback). If you need authoritative behavior for unusual prefixes, verify against a trusted networking tool or library.

CIDR Calculator

Given an IP address in CIDR notation, compute all subnet parameters: network address, broadcast, host range, subnet mask, wildcard mask, host counts, IP class, and binary representation.

Input

• A CIDR notation string in the format A.B.C.D/N (e.g. 192.168.1.0/24)

Output

A structured result with these fields:

• CIDR Notation (normalized)
• Network Address
• Broadcast Address
• Subnet Mask
• Wildcard Mask
• First Usable Host
• Last Usable Host
• Total Hosts (2^(32-N))
• Usable Hosts
• IP Class (A / B / C / D Multicast / E Reserved)
• Network Type (Private / Public)
• Binary Representation of the IP

Instructions

1. Validate the input. It must match \d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}\/\d{1,2}. Each octet must be 0–255. Prefix must be 0–32.
2. Compute values using standard subnet math:
   • maskNum = (0xFFFFFFFF << (32 - prefix)) >>> 0
   • wildcardNum = ~maskNum >>> 0
   • networkNum = (ipNum & maskNum) >>> 0
   • broadcastNum = (networkNum | wildcardNum) >>> 0
   • totalHosts = 2^(32 - prefix)
   • usableHosts: if prefix == 32 → 1; if prefix == 31 → 2; else totalHosts - 2
3. Determine IP class from first octet:
   • 1–126 → A; 128–191 → B; 192–223 → C; 224–239 → D (Multicast); 240–255 → E (Reserved); 127 → Loopback
4. Determine private vs public:
   • Private: 10.x.x.x, 172.16–31.x.x, 192.168.x.x, 127.x.x.x (loopback)
5. Compute binary as four 8-bit groups joined by dots.
6. Present results in a clear labeled format.

Quick CIDR reference

CIDR	Subnet Mask	Total Hosts
/8	255.0.0.0	16,777,216
/16	255.255.0.0	65,536
/20	255.255.240.0	4,096
/22	255.255.252.0	1,024
/24	255.255.255.0	256
/28	255.255.255.240	16
/30	255.255.255.252	4
/32	255.255.255.255	1

Options

• Input is always a single CIDR string; no additional options.

Examples

Input: 192.168.1.0/24

Output:

CIDR Notation:   192.168.1.0/24
Network Address: 192.168.1.0
Broadcast:       192.168.1.255
Subnet Mask:     255.255.255.0
Wildcard Mask:   0.0.0.255
First Host:      192.168.1.1
Last Host:       192.168.1.254
Total Hosts:     256
Usable Hosts:    254
IP Class:        C
Network Type:    Private
Binary:          11000000.10101000.00000001.00000000

Input: 10.0.0.0/8

Output:

CIDR Notation:   10.0.0.0/8
Network Address: 10.0.0.0
Broadcast:       10.255.255.255
Subnet Mask:     255.0.0.0
Wildcard Mask:   0.255.255.255
First Host:      10.0.0.1
Last Host:       10.255.255.254
Total Hosts:     16,777,216
Usable Hosts:    16,777,214
IP Class:        A
Network Type:    Private
Binary:          00001010.00000000.00000000.00000000

Error Handling

• If the input is not valid CIDR notation, say so and provide the expected format (A.B.C.D/N).
• If an octet exceeds 255 or the prefix exceeds 32, explain the validation error.
• If the user provides an IP without a prefix (e.g. 192.168.1.1), ask for the prefix length or assume /32.