FW Blacklist Checker

What is it

The FW DNS Blacklist Checker is a free, fully client-side tool that checks if an IP address or domain is listed in public blacklists (RBLs/DNSBLs) used by email servers, firewalls, and security systems worldwide.

How it works

The tool automatically performs the following steps:

• You enter an IP (e.g., 1.2.3.4) or domain (e.g., example.com).
• If it's a domain, it's resolved to IP via DNS-over-HTTPS (DoH).
• The IP is reversed (e.g., 4.3.2.1) and queried against each blacklist.
• Each query is made in the format reversed-IP.blacklist-zone.
• If the response is 127.0.0.x, the IP is LISTED.
• If there's no response (NXDOMAIN), the IP is CLEAN on that list.

Where queries are made

All DNS queries are performed via public DNS-over-HTTPS (DoH) from Google (dns.google), ensuring:

• Encrypted queries (HTTPS).
• No own server involved — everything happens in your browser.
• High availability and low latency.
• No logs are stored by this tool.

Blacklists checked ()

The tool queries the following public DNSBLs/RBLs:

Advantages

• Totally free — no paid plans, no premium version.
• No query limits — use as many times as you need.
• No registration or login — open and use.
• No installation — works directly in the browser.
• Real-time results — cards update as queries return.
• Local history — your last queries are saved in your browser.
• Quick export — copy listed results with one click.

Technical Limits

• DoH Rate limit: Google may limit very intensive queries. The tool uses 6 parallel queries to avoid blocks.
• Timeout: each query has a 5-second timeout. Slow blacklists may appear as "error".
• IPv6: currently only supports IPv4.
• URIBLs: URL domain-based lists (like SURBL) are not queried in this version.
• Accuracy: some blacklists may have false positives — always check the official list website.
• Query only: this tool does not remove your IP from blacklists. For removal, access each list's official website.

How to interpret results

• ✅ Clean: the IP is not listed on this blacklist.
• ❌ LISTED: the IP is on the blacklist. The code 127.0.0.x indicates the reason (varies by list).
• ⚠️ Error: could not query (timeout or blacklist offline).

Technology

Tool developed in HTML5 + CSS3 + pure JavaScript, without backend dependencies. Uses Fetch API, Promise.all with chunks for parallelization, AbortController for timeouts, and localStorage for local history.