CIDR Calculator API

Calculate network, broadcast, subnet mask and host counts from CIDR notation, or summarize any IP range into minimal CIDR blocks. IPv4 + IPv6 — free.

The CIDR Calculator is also available as a free REST API. Send a POST request with a JSON body to https://dot.tools/api/tools/cidr-calculator — no authentication, no API key, CORS enabled. Successful calls return { "ok": true, "result": { … } }; failures return HTTP 400 or 422 with an error body.

Request body

Field	Type	Required	Description
`mode`	"cidr" \| "range"	required	"cidr" analyzes one CIDR block (network, broadcast, masks, host counts). "range" summarizes an arbitrary start-end IP range into the minimal set of CIDR blocks.
`cidr`	string	optional	Required when mode is "cidr". IPv4 or IPv6 CIDR notation, e.g. "192.0.2.0/24" or "2001:db8::/32". IPv4 rejects leading zeros and short/hex forms; IPv6 accepts one "::" compression and embedded IPv4 tails.
`normalize`	boolean	optional	When false (default), a CIDR with host bits set (e.g. "10.0.0.1/8") fails with errorCode HOST_BITS_SET and a suggestion field carrying the network CIDR. When true, the address is masked to its network and the result has normalized=true.
`start`	string	optional	Required when mode is "range". First address of the range, IPv4 or IPv6.
`end`	string	optional	Required when mode is "range". Last address of the range, same family as start and not smaller.

Response

Field	Type	Required	Description
`family`	unknown	required	Detected address family, null on error.
`error`	unknown	required	Human-readable error message, null on success.
`errorCode`	unknown	required	Machine-readable error code such as HOST_BITS_SET, INVALID_CIDR, FAMILY_MISMATCH or RANGE_ORDER.
`suggestion`	unknown	required	On HOST_BITS_SET, the normalized network CIDR to retry with (or pass normalize=true).
`cidr`	unknown	required	The normalized CIDR that was analyzed (cidr mode).
`network`	unknown	required	Network (first) address of the block.
`broadcast`	unknown	required	Broadcast address. IPv4 /30 and shorter only — null for IPv6, /31 (RFC 3021) and /32.
`firstUsable`	unknown	required	First usable host address.
`lastUsable`	unknown	required	Last usable host address.
`totalHosts`	unknown	required	Total addresses in the block, as a decimal string (can exceed 2^53).
`usableHosts`	unknown	required	Usable host addresses as a decimal string: total-2 for IPv4 /30 and shorter, 2 for /31, 1 for /32; total for IPv6, 2 for /127, 1 for /128.
`subnetMask`	unknown	required	Dotted subnet mask, IPv4 only.
`wildcardMask`	unknown	required	Dotted wildcard (inverse) mask, IPv4 only.
`normalized`	boolean	required	True when the input had host bits set and was masked to its network address.
`rangeStart`	unknown	required	Start address of the analyzed range (range mode).
`rangeEnd`	unknown	required	End address of the analyzed range (range mode).
`rangeCount`	unknown	required	Number of addresses in the range, as a decimal string.
`cidrs`	unknown	required	Minimal exact CIDR decomposition of the range (range mode).

Example request

curl -X POST https://dot.tools/api/tools/cidr-calculator \
  -H 'Content-Type: application/json' \
  -d '{
  "mode": "cidr",
  "cidr": "192.168.0.0/24"
}'

Sample response

{
  "ok": true,
  "result": {
    "family": "ipv4",
    "error": null,
    "errorCode": null,
    "suggestion": null,
    "cidr": "192.168.0.0/24",
    "network": "192.168.0.0",
    "broadcast": "192.168.0.255",
    "firstUsable": "192.168.0.1",
    "lastUsable": "192.168.0.254",
    "totalHosts": "256",
    "usableHosts": "254",
    "subnetMask": "255.255.255.0",
    "wildcardMask": "0.0.0.255",
    "normalized": false,
    "rangeStart": null,
    "rangeEnd": null,
    "rangeCount": null,
    "cidrs": null
  }
}

Use the free CIDR Calculator in your browser, read the CIDR Calculator guide, or import the full OpenAPI specification.