Enter an IPv4 address or CIDR range and see if it appears in active FireHOL or selected third-party blocklists. Useful for checking server IP reputation, investigating abuse reports, reviewing suspicious traffic / debugging abuse-related network issues.
The indexed lists are refreshed multiple times a day. API rate limits apply. Allowed CIDR prefix range /16 through /32. Last sync 2026-09-13 15:55 UTC.
Mail RBL checks are mainly useful for email blacklist checks and delivery issues. This API checks IP blocklists sourced primarily from the FireHOL IP Lists project (along with a small selection of third-party lists indexed directly). These cover broader security signals such as scanners, abuse, malware, botnets, proxies and attack sources.
For matching IPs, the API shows which blocklists contain the address, maintainer and source information where available, when it was first seen and last seen, and if the match was based on the IP itself or a larger network range (CIDR). Historical results can also show if an IP was listed before but is no longer active.
FireHOL collects n publishes many different types of IP lists. Our API focuses only on active security-related IP blocklists, indexes their blocklists, stores historical data, and makes the information easy to search and query. We do not maintain the original lists and cannot remove any IPs from them. You can also view the indexed blocklists currently used by this search.
Want to suggest or add your own blocklist? Contact blocklist [at] sernate [dot] com.
A blocklist listing is an indication, not a verdict. Different blocklists track different types of activity, and not every provider uses the same lists. A match can be useful when investigating mail delivery, abuse, reputation or connectivity issues, but being listed does not by itself explain the cause or mean the IP is actively being blocked. Always check what the list monitors and why the IP appears on it.
If you want to monitor your own server or IP space, you can use our API to check a single IP address, a CIDR range or a small batch of addresses from your own scripts or monitoring tools.
For DirectAdmin servers, we also maintain a DirectAdmin plugin that checks the server’s public IPv4 IP(s) against the blocklists indexed here.