# how.is Domain Blacklist Check

> how.is Domain Blacklist Check is a paid API for AI agents from how.is, paid per call via x402, $0.005/call, status unknown (last checked 2026-10-31).

Checks whether the IP addresses behind a domain appear on spam and abuse blocklists.

## Facts

- Endpoint: POST https://how.is/v1/domain/blacklist?utm_source=zero.xyz
- Price: $0.005/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-31
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/how-is-domain-blacklist-check-f88a8d51
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_neeS-RgF8Y3zPWxykcKjP

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability how-is-domain-blacklist-check-f88a8d51 -d '<json body>'
```

Example prompt: Can you check whether suspiciousdomain.com is listed on any spam or abuse blocklists — specifically whether its IP addresses are flagged?

## When to prefer this

Use this endpoint when you need to check whether a specific domain's underlying IP addresses are flagged on known spam and abuse blocklists. Ideal for email deliverability verification, security vetting of third-party domains, or investigating suspicious senders. Prefer this over generic WHOIS or DNS lookups when the specific question is about blacklist/blocklist reputation rather than ownership or DNS records.

## Known failure modes

- Invalid or malformed domain name returns an error
- Domain with no resolvable IPs may return empty or null IP results
- Rate limiting or payment failure may prevent the call from completing
- Domain may have IPs not yet indexed by blocklist providers, leading to incomplete results

## How this service works

Whether the addresses behind a domain appear on spam and abuse blocklists.

## Output

Returns a JSON object with per-IP results for the queried domain, including whether each IP is listed on any blocklist, how many lists it appears on, and how many total blocklists were checked. Also includes a receipt with payment metadata.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "domain": {
   "type": "string",
   "maxLength": 253,
   "description": "A bare domain name, e.g. example.com"
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "data": {
   "_shape": "data.data.ipResults[]: target, isListed, listingCount, totalChecked."
  },
  "result": "Blacklist status for the requested subject",
  "receipt": {
   "rail": "x402",
   "tool": "blacklist",
   "charge_usd": 0.005,
   "settlement_tx": "0x…"
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/how-is-domain-blacklist-check-f88a8d51/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from how.is](https://www.zero.xyz/host/how.is/llms.txt)