# IPv4 mask convert

`ipv4-mask-convert` · version 1.0.0 · URLs & IP addresses · free, no key needed

Convert between an IPv4 prefix length, dotted subnet netmask, and dotted wildcard (host) mask.

**Use when you need to: ipv4 mask convert · prefix to netmask · netmask to prefix.**

## Supported

- ipv4 mask convert
- prefix to netmask
- netmask to prefix
- wildcard mask convert
- subnet mask calculator

## Not supported

- IPv6
- non-contiguous masks

## Behavior

- Input is exactly one of prefix, netmask, or wildcard; unknown fields and multiple/zero of these three throw.
- prefix is a JSON integer 0-32.
- netmask must be a contiguous run of 1-bits from the most significant bit followed by 0-bits (a valid subnet mask); otherwise the tool throws.
- wildcard is the bitwise complement of a valid netmask (a contiguous run of 0-bits followed by 1-bits); otherwise the tool throws.
- Output always includes all three equivalent representations.

## Input

- object

## Output

- `prefix` (integer, required): min 0; max 32
- `netmask` (string, required): max length 15
- `wildcard` (string, required): max length 15

## Limits

- prefix min: 0
- prefix max: 32

## Example

Request input:

```json
{
  "prefix": 24
}
```

Response:

```json
{
  "result": {
    "prefix": 24,
    "netmask": "255.255.255.0",
    "wildcard": "0.0.0.255"
  }
}
```

## How to call it

### MCP

Connect `https://computefirst.net/mcp` ([setup](/docs#connect)), then call `execute` with:

```json
{
  "id": "ipv4-mask-convert",
  "version": "1.0.0",
  "input": {
    "prefix": 24
  }
}
```

### HTTP (no key)

```sh
curl -X POST https://computefirst.net/v1/tools/ipv4-mask-convert/versions/1.0.0/execute \
  -H "Content-Type: application/json" \
  -d '{"prefix":24}'
```

The machine-readable contract is at [/v1/tools/ipv4-mask-convert/versions/1.0.0](/v1/tools/ipv4-mask-convert/versions/1.0.0).

### CLI

```sh
node cli.mjs run ipv4-mask-convert 1.0.0 --input input.json --base-url https://computefirst.net
```

Get the client at [/clients/cli/](/clients/cli/).

## Related tools

- [IPv4 CIDR parse](/tools/ipv4-cidr-parse): Parse an IPv4 CIDR block into its network, broadcast, netmask, wildcard mask, usable host range and address counts.
- [IPv4 prefix for hosts](/tools/ipv4-prefix-for-hosts): Compute the smallest IPv4 CIDR block (largest prefix length) whose usable host capacity meets a required count.
- [IPv4 range to cidrs](/tools/ipv4-range-to-cidrs): Convert an arbitrary IPv4 address range into the minimal list of CIDR blocks that exactly covers it.
- [IPv4 address offset](/tools/ipv4-address-offset): Add a signed integer offset to an IPv4 address, throwing if the result leaves the IPv4 address space.
- [IPv4 CIDR contains](/tools/ipv4-cidr-contains): Test whether one IPv4 CIDR block fully contains another IPv4 CIDR block.
- [IPv4 CIDR overlap](/tools/ipv4-cidr-overlap): Test whether two IPv4 CIDR blocks overlap (share at least one address).