DNSBL API

Getting started

Subscribe, copy your secret key, and run your first DNSBL lookup.

The Syndaq DNSBL API checks public IPv4 addresses against major open DNS blacklist zones. Responses include a boolean listed flag, the matching list entries, and how many zones reported a hit.

What you need

  1. A DNSBL plan from the Syndaq API catalog.
  2. A secret key (bl_sec_) from the Syndaq client area after your order is provisioned.

DNSBL lookups are server-side only. Send your secret key from your backend or trusted worker. Do not embed it in client-side code, mobile apps, or public repositories.

Base URL

All DNSBL endpoints are served from:

https://api.syndaq.com/v1/dnsbl/

Quick start

Replace bl_sec_YOUR_SECRET_KEY with the secret shown in Services for your DNSBL subscription.

curl -sS "https://api.syndaq.com/v1/dnsbl/lookup/8.8.8.8" \
  -H "Authorization: Bearer bl_sec_YOUR_SECRET_KEY"

You can also pass the IP as a query parameter:

curl -sS "https://api.syndaq.com/v1/dnsbl/lookup?ip=8.8.8.8" \
  -H "Authorization: Bearer bl_sec_YOUR_SECRET_KEY"

A successful response includes listed, list_count, the lists array of matching zones, and how many zones were checked.

How lookups work

StepWhat happens
1Authenticate with your secret key.
2Send a lookup request to the API.
3Receive JSON with the result fields (including a cached flag when Syndaq already holds a recent result).

IPv4 only. IPv6 addresses are rejected with a clear error. Private, reserved, and invalid addresses also return an error.

Manage your subscription

Sign in to the Syndaq client area and open Services. Select your DNSBL service to:

  • View usage and remaining monthly quota
  • Copy or rotate your secret key
  • Configure optional IP allowlists for API access

Next steps