# IP.THC.ORG

> IP.THC.ORG is a free service for searching the world's largest Internet domain
> database — 5.90 billion+ indexed domains. It provides Reverse DNS (rDNS) lookup,
> a Subdomain finder, and CNAME lookup, available through a web interface, plain-text
> endpoints, a JSON REST API, and CSV bulk downloads. No registration or API key is
> required, and the service will always remain free.

Base URL: `https://ip.thc.org`

## What you can do

- **Reverse DNS lookup** — given an IP address or CIDR range, list every domain known to resolve to it (with ASN, organization, city, and country). Example: `curl https://ip.thc.org/1.1.1.1`
- **Subdomain finder** — given an apex domain, enumerate its known subdomains. Example: `curl https://ip.thc.org/sb/thc.org`
- **CNAME lookup (reverse)** — given a target hostname, find every domain whose CNAME points to it. Useful for mapping SaaS tenants and detecting subdomain-takeover risk. Example: `curl https://ip.thc.org/cn/github.io`

## Key facts

- **Free forever**, no registration and no API key required.
- **Database size**: 5.90 billion+ indexed domains (the largest free Internet domain database).
- **Rate limits**: 250-token burst, 0.5 tokens/sec refill, per IP. Bulk downloads cost 3 tokens; standard lookups cost 1. Exceeding the limit returns HTTP 429.
- **Output formats**: ANSI/plain text, JSON, and CSV (bulk, up to 50,000 records per request).
- **Maintained by**: The Hacker's Choice (hackerschoice).

## API quick reference

- Reverse DNS (text): `curl https://ip.thc.org/1.1.1.1?nocolor=1`
- Subdomains (text): `curl https://ip.thc.org/sb/thc.org?nocolor=1`
- CNAMEs (text): `curl https://ip.thc.org/cn/github.io?nocolor=1`
- Reverse DNS (JSON): `POST https://ip.thc.org/api/v1/lookup` with `{"ip_address":"8.8.8.0/24","limit":10}`
- Subdomains (JSON): `POST https://ip.thc.org/api/v1/lookup/subdomains` with `{"domain":"thc.org","limit":10}`
- CNAMEs (JSON): `POST https://ip.thc.org/api/v1/lookup/cnames` with `{"target_domain":"google.com","limit":10}`
- CSV bulk: `https://ip.thc.org/api/v1/download?ip_address=8.8.8.8&limit=500`

## Bulk data download

For large-scale or offline use, data can be exported in bulk rather than one lookup at a time:

- **Per-query CSV** — up to 50,000 records per request, for each lookup type:
  - Reverse DNS: `https://ip.thc.org/api/v1/download?ip_address=8.8.8.8&limit=500`
  - Subdomains: `https://ip.thc.org/api/v1/subdomains/download?domain=thc.org&limit=500`
  - CNAMEs: `https://ip.thc.org/api/v1/cnames/download?target_domain=google.com&limit=500`
  - Optional params: `hide_header=true` to omit CSV headers, `apex_domain` and `tld[]` to filter.
- **Full-dataset snapshots** — the complete database is available for download in CSV and Parquet format for offline analysis. See [bulk data access](https://ip.thc.org/docs/bulk-data-access).
- Bulk download requests consume 3 rate-limit tokens (standard lookups consume 1).

## Documentation

- [Full API reference](https://ip.thc.org/llms-full.txt): every endpoint, parameter, and response schema in detail.
- [API docs](https://ip.thc.org/docs/): human-readable documentation.
- [Reverse DNS lookup API](https://ip.thc.org/docs/API/reverse-dns-lookup)
- [Subdomain lookup API](https://ip.thc.org/docs/API/subdomain-lookup)
- [CNAME lookup API](https://ip.thc.org/docs/API/cname-lookup)
- [Bulk data access](https://ip.thc.org/docs/bulk-data-access)
- [CLI usage](https://ip.thc.org/docs/cli)

## Support

The service is free and community-funded. Donations (BTC/ETH/XMR) and bulk-access or
partnership inquiries are welcome via Telegram: https://t.me/thcorg