About IPv4Scanner

IPv4Scanner is a free set of network and domain tools, and a library of plain-English guides explaining what the results mean. It is built for the people who end up debugging the internet without it being their full-time job: developers, site owners, small-business IT, students, and anyone who has been told to "check the DNS" and wants to know what that involves.

Every tool is free, needs no account, and returns its answer on the page. Nothing is hidden behind a sign-up or an email capture.

The tools

There are 29 tools at the moment:

• Domain Health Report — One report: expiry, certificate, DNS, email authentication and reputation.
• IP Location Finder — Geolocation, ISP and network details for any IP address.
• Website WHOIS — Registration and ownership details for a domain.
• DNS Lookup — A, AAAA, MX, TXT and NS records for a domain.
• Reverse DNS / PTR — Find the PTR hostname(s) for an IP address.
• DNS Propagation Check — Check a DNS change against ten resolvers and probes on six continents.
• Global Ping Test — Round-trip time and packet loss to a host, measured from six continents.
• Global Traceroute — The hop-by-hop network path to a host, traced from six continents.
• Global HTTP Check — Whether a site is up, and how fast it answers, from six continents.
• SPF, DKIM & DMARC Checker — Validate the three DNS records that decide whether your email is trusted.
• SPF Record Generator — Build one valid SPF record for every service that sends your email, inside the 10-lookup limit.
• DMARC Record Generator — Create a DMARC policy step by step and check your reports will actually arrive.
• Security Headers Checker — Grade a site's HSTS, CSP and other security headers, with the exact fix for each gap.
• Redirect Checker — Trace every redirect hop, and check http, https and www all end in one place.
• CAA Record Generator — Limit which certificate authorities may issue SSL certificates for your domain.
• Port Number Reference — What the common TCP and UDP ports are for, and whether each is safe to leave open.
• IP Blacklist Check — Check an IP against six public DNS blocklists, including SpamCop and Barracuda.
• SSL/TLS Certificate Checker — Inspect a domain certificate: issuer, expiry, SAN, trust.
• Domain Age — Domain registration date, age, expiry and registrar.
• Uptime Monitor — Live status and uptime history for monitored sites.
• Subnet / CIDR Calculator — Network, broadcast, mask, host range and counts for a CIDR block.
• Port Scanner — Check common TCP ports on a host.
• WebRTC Leak Test — See if your browser leaks your real IP via WebRTC.
• User-Agent Viewer — Your user-agent string and browser fingerprint.
• Internet Speed Test — Measure your download and upload speed.
• Hash Generator — MD5, SHA-1 and SHA-256/384/512 hashes of any text, in your browser.
• Base64 & URL Encoder — Encode and decode Base64 and URL-encoded text, Unicode-safe.
• Password Generator — Strong random passwords from your device's cryptographic RNG.
• JSON Formatter — Format, validate and minify JSON, with line-and-column error reports.

Alongside them is a reference to the common port numbers, covering what each one is for, how to test it and what to do if it is exposed, and a blog of guides that go into the subjects behind the tools.

Where the results come from

The tools query live systems when you press the button. Nothing is served from a stale database of old scans.

• DNS, reverse DNS, blacklists and email authentication are resolved in real time from our server, against public resolvers and the DNS-based blocklists themselves (for example Spamhaus ZEN and Barracuda).
• Global ping, traceroute, HTTP checks and DNS propagation run from volunteer probes on six continents through the open Globalping network, so you see how a host looks from outside your own network rather than only from ours.
• IP geolocation comes from the DB-IP Lite databases, which we keep on our own server and refresh every month, so a lookup never depends on a third-party service being up.
• WHOIS and domain age come from registry and registrar records.
• SSL, HTTP and port checks connect directly to the host you name, the same way a browser or client would.
• The hash, Base64, password and JSON tools run entirely in your browser. What you type into them is never sent to us.

Maps are drawn with OpenStreetMap data.

How accurate it is

Most results here are facts read directly from the source: a DNS record, a certificate's expiry date, whether a port answered. Those are as accurate as the system being queried.

IP geolocation is different. It is an estimate, and it is usually right about the country, often right about the city, and rarely precise enough to find a street. Mobile networks, VPNs and corporate gateways routinely place people in the wrong city. The tools say so where it matters, and this guide explains why.

How the guides are written

Each guide is written to answer a question people actually bring to these tools, such as why an email went to spam, what a traceroute's asterisks mean, or whether a ping of 80 ms is good. They are checked against the relevant standards and against the tools' real output, and are corrected when something changes or turns out to be wrong. If you spot an error, tell us and it will be fixed.

Privacy

Lookups are not tied to an account because there are no accounts. Blog comments and votes are linked to a salted hash of your IP address, never the address itself, and the client-side tools never send your input anywhere. The privacy policy has the detail.

How the site is paid for

IPv4Scanner is supported by advertising. That pays for the servers and the commercial data the lookups depend on, and it is why the tools can stay free without limits or sign-ups. Advertisers have no say over what the tools report or what the guides say.

Get in touch

Bug reports, corrections and requests for new tools are all welcome. Use the contact form.