# is-valid-domain

A CLI tool to validate domain names using the public suffix list from `golang.org/x/net/publicsuffix`.

## Usage

```bash
./is-valid-domain <domain>
```

## Examples

```bash
./is-valid-domain 029.cyou          # Output: valid
./is-valid-domain siliconpin.co.in   # Output: valid
./is-valid-domain co.siliconpin.in   # Output: subdomain
./is-valid-domain invalid..domain    # Output: invalid
```

## Output Categories

- **valid** - The domain is a registrable domain (effective TLD+1)
- **subdomain** - The domain is a subdomain of a registrable domain
- **invalid** - The domain is malformed or not a valid domain name

## Installation

```bash
go build -o is-valid-domain main.go
```

## How it Works

The tool uses `publicsuffix.EffectiveTLDPlusOne()` to determine the registrable domain:

1. If the input domain exactly matches the effective TLD+1 → **valid**
2. If the input domain is longer than the effective TLD+1 → **subdomain**
3. If there's an error parsing the domain → **invalid**

This leverages the official public suffix list to correctly handle complex TLD structures like `.co.in`, `.co.uk`, etc.