A practical roundup. We focus on APIs that answer "should I let this IP sign up / post / buy" with a clear yes/no and a reason.
One call: 7 DNSBLs (Spamhaus ZEN, Spamcop, Barracuda, CBL, SORBS, UCEPROTECT L1, PSBL) + ASN + geo + proxy/hosting/mobile flags. Composite 0-100 score, low/medium/high risk. 100 free calls/day, no signup.
Best for: signup forms, comment systems, login attempt scoring. Try it · vs IPinfo
Industry standard for fraud detection. Has all the basics plus device fingerprinting, email verification, phone validation, transaction scoring. Free tier is 5,000 lookups/mo. Paid from $37/mo for 50k.
Best for: e-commerce fraud, enterprise risk scoring, teams that need the full fraud platform.
Best-in-class geolocation, plus their own privacy/threat feed. Doesn't do DNSBLs directly but has proxy/VPN/TOR detection. Free tier is 50,000 requests/mo. Paid from $49/mo.
Best for: when you need deep geo + a reputation signal in one call. Comparison with sitetrace
The organization that maintains most of the public DNSBLs also offers a commercial data feed. More accurate than the public DNSBL queries (real-time updates, fewer false positives), with more list coverage. Free for low-volume use; commercial pricing on request.
Best for: mail server operators, anyone whose false-positive cost is high.
Different angle: maps an IP to the organization responsible for it and their abuse contact. Useful for "I need to report spam from this IP". Free API, by URLhaus/abuse.ch.
Best for: security teams doing incident response, not for real-time signup decisions.
| Use case | Pick |
|---|---|
| Block fake signups on a SaaS | sitetrace, IPQS |
| E-commerce fraud scoring | IPQS (their model is tuned for this) |
| "Where is this user from" + reputation | IPinfo |
| Mail server, low false-positive tolerance | Spamhaus Data Feed |
| Abuse / incident response | AbuseIPDB |
| Cheapest possible: hobby projects | sitetrace (free tier, no card) |