Netmask to CIDR Converter API: The Complete Guide

Need to convert subnet masks to CIDR notation? This guide covers everything about netmask to CIDR conversion via API, including common netmask values, the conversion process, and implementation examples.

Understanding Netmasks

A subnet mask (netmask) defines which portion of an IP address represents the network and which represents the host. It's traditionally written in dotted-decimal format like 255.255.255.0.

Common netmask to CIDR mappings:

• 255.0.0.0 = /8
• 255.255.0.0 = /16
• 255.255.255.0 = /24
• 255.255.255.128 = /25
• 255.255.255.192 = /26

The Conversion Process

The CIDR prefix is simply the count of contiguous 1-bits in the netmask:

255.255.255.0 in binary:
11111111.11111111.11111111.00000000

Count of 1s = 24, so CIDR = /24

Using the Netmask to CIDR API

TinyFn provides a simple endpoint for netmask conversion:

GET https://api.tinyfn.io/v1/ip/netmask-to-cidr?netmask=255.255.255.0
Headers: X-API-Key: your-api-key

{
  "netmask": "255.255.255.0",
  "cidr": 24,
  "binary": "11111111111111111111111100000000",
  "wildcard": "0.0.0.255",
  "hosts": 254
}

Parameters

Code Examples

JavaScript / Node.js

const response = await fetch(
  'https://api.tinyfn.io/v1/ip/netmask-to-cidr?netmask=255.255.255.0',
  { headers: { 'X-API-Key': 'your-api-key' } }
);
const { cidr } = await response.json();
console.log(`CIDR: /${cidr}`); // "CIDR: /24"

Python

import requests

response = requests.get(
    'https://api.tinyfn.io/v1/ip/netmask-to-cidr',
    headers={'X-API-Key': 'your-api-key'},
    params={'netmask': '255.255.255.0'}
)
cidr = response.json()['cidr']
print(f"CIDR: /{cidr}")  # "CIDR: /24"

cURL

curl "https://api.tinyfn.io/v1/ip/netmask-to-cidr?netmask=255.255.255.0" \
  -H "X-API-Key: your-api-key"

Common Use Cases

• Configuration Migration: Convert old-style configs to CIDR format
• Network Documentation: Standardize network documentation
• API Integration: Translate between systems using different formats
• Firewall Rules: Convert netmasks for modern firewall syntax
• Cloud Networking: Prepare network configs for cloud providers

Best Practices

1. Validate netmasks: Ensure netmasks are valid before conversion
2. Standardize on CIDR: CIDR is the modern standard; migrate to it
3. Document conversions: Keep a reference table for common conversions
4. Handle both formats: Accept both netmask and CIDR in your applications

Use via MCP

Your AI agent can call this tool directly via Model Context Protocol — no HTTP code needed. Add TinyFn to Claude Desktop, Cursor, or any MCP client:

{
  "mcpServers": {
    "tinyfn-ip": {
      "url": "https://api.tinyfn.io/mcp/ip/",
      "headers": {
        "X-API-Key": "your-api-key"
      }
    }
  }
}

See all ip address tools available via MCP in our IP Address MCP Tools for AI Agents guide.