is-valid-domain

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

Usage

./is-valid-domain <domain>

Examples

./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

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.