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domain-availability-checker.underscoredone.com check
https://domain-availability-checker.underscoredone.com/check
answers 402
Give this API up to 10 domain names and it will tell you whether each one has a registration record on file with the official registry. It uses RDAP — the modern, structured replacement for WHOIS — so there is no messy free-text parsing. Each domain comes back labeled 'registered', 'unregistered', or 'indeterminate' (when the registry does not support RDAP for that ending). Important: 'unregistere
We sent a real
POST request to this endpoint and it
answered 402 with payment requirements we could parse.
- Price
- $0.01
- Network
- base
- Pay to
- 0xE9740820225B3918b4ddd1292C7cA4Ca0e2C2F08
- Spec dialect
- v2 (declares x402Version 2)
- Transport
- PAYMENT-REQUIRED header
- HTTP method
- POST
- Response latency
- 154 ms
- Payment options
- 2 usable of 2
- Last checked
- 2026-08-15T14:22:18.685Z (1h ago)
- Category
- finance-crypto
Re-check it yourself:
curl "https://api.the402.dev/validate?url=https%3A%2F%2Fdomain-availability-checker.underscoredone.com%2Fcheck"