Give this API up to 10 domain names and it tells you whether each has a registra
Give this API up to 10 domain names and it tells you whether each has a registration record at the official registry. It uses RDAP, the structured replacement for WHOIS, so there is no free-text parsing. Each domain comes back as 'registered', 'unregistered', or 'indeterminate' when the registry has no RDAP for that ending. 'Unregistered' means no record was found, which usually means available - but reserved and premium names also return no record. Registration status only; no pricing.
Paid test badge: not yet. The checks above are free: we call the tool without paying and read the payment request it sends back. The Verified badge needs paid calls whose answers match the promised output, and nobody can buy a badge.
Endpoint
POST https://domain-availability-checker.underscoredone.com/check
| Category | Company and compliance |
|---|---|
| Provider host | domain-availability-checker.underscoredone.com |
| Networks | eip155:8453, solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp |
| Payment schemes | exact |
| Self-reported calls, 30 days | 3 from 3 payers (the provider's figure, not ours) |
Our checks, last 30 days
| Day | Result | HTTP | Asked | Time |
|---|---|---|---|---|
| 2026-09-24 | valid payment request | 402 | $0.01 | 828 ms |
Example input (from the provider)
{
"body": {
"domains": [
"example.com",
"mybrand.ai",
"coolstartup.io"
]
},
"bodyType": "json",
"method": "POST",
"type": "http"
}
Promised output schema (from the provider)
{
"$schema": "https://json-schema.org/draft/2020-12/schema",
"properties": {
"input": {
"additionalProperties": false,
"properties": {
"body": {
"additionalProperties": false,
"properties": {
"domains": {
"description": "Between 1 and 10 domain names to check, like 'example.com' or 'mybrand.ai'. Use the plain registrable domain only \u2014 no 'https://', no 'www.', no subdomains.",
"type": "array"
}
},
"required": [
"domains"
],
"type": "object"
},
"bodyType": {
"enum": [
"json",
"form-data",
"text"
],
"type": "string"
},
"method": {
"enum": [
"POST",
"PUT",
"PATCH"
],
"type": "string"
},
"type": {
"const": "http",
"type": "string"
}
},
"required": [
"type",
"method",
"bodyType",
"body"
],
"type": "object"
},
"output": {
"properties": {
"example": {
"properties": {
"api_version": {
"type": "string"
},
"count": {
"type": "integer"
},
"disclaimer": {
"type": "string"
},
"queried_at": {
"type": "string"
},
"results": {
"items": {
"type": "object"
},
"type": "array"
}
},
"required": [
"count",
"results",
"queried_at",
"disclaimer",
"api_version"
],
"type": "object"
},
"type": {
"type": "string"
}
},
"required": [
"type"
],
"type": "object"
}
},
"required": [
"input"
],
"type": "object"
}