CIDR calculator API: network, broadcast, hosts and netmask

$0.01 per call · failed calls are never charged · no account or subscription: pay per call with a card key or USDC

Details of an IPv4 network in CIDR notation: network and broadcast address, first and last usable host, netmask, number of addresses, and whether a given IP falls inside. Use for firewall rules and allowlists.

When to use it

Build firewall rules and allowlists
Get the network and broadcast address, first and last usable host, netmask and address count
Check whether a given IP falls inside the range

Run it free (25 free calls) Buy credits by card (from $1) Example result (JSON)

Inputs

Name	Type	Description
`cidr` (required)	string	IPv4 network in CIDR notation
`ip`	string	Optional IPv4 address to test for membership

Request

Over HTTP, with a card key from /credits:

curl -H "Authorization: Bearer adt_…" "https://tools.funwords.eu/ip/cidr?cidr=192.168.1.0%2F24"

Or one of your 25 free calls, no key:

curl "https://tools.funwords.eu/ip/cidr?cidr=192.168.1.0%2F24&trial=1"

Without a key, the same URL answers 402 Payment Required with x402 and MPP terms, so an agent with a wallet pays per call in USDC (Base, Polygon, Arbitrum or Solana over x402; Base or Tempo over MPP) and retries.

Example result

{
  "network": "192.168.1.0",
  "broadcast": "192.168.1.255",
  "first": "192.168.1.1",
  "last": "192.168.1.254",
  "prefix": 24,
  "netmask": "255.255.255.0",
  "addresses": 256,
  "usableHosts": 254,
  "contains": true
}

From an AI agent (MCP)

Add the MCP server to Claude, Cursor or any MCP client. This tool is ip_cidr, and the first 25 successful calls are free:

https://tools.funwords.eu/mcp

Questions

IPv6 too?

No, IPv4 networks in CIDR notation.

How do I pay?

Each successful call costs $0.01; failed calls are not charged. The first 25 calls are free. Then pay with card credits (from $1; the key goes in an Authorization header or, for clients that can only fetch a URL, as api_key= in the URL) or per call in USDC over x402 or MPP. No account is needed.