init

README.md

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+# 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.