IP · DNS · HTTP · PORT
Network Diagnostic Tool – Check IP, DNS, HTTP & TCP Ports Online
Look up IPs, inspect DNS, check HTTP responses and test TCP ports — fast, accurate and free.
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IPv4
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Everything you need to inspect and troubleshoot networks.
What Is a Network Diagnostic Tool?
A network diagnostic tool is a set of utilities that answer the everyday questions about a connection: what public IP address am I using, what does a domain resolve to, is a server reachable, and is a particular port open. TCPLab runs these checks from real servers rather than your browser alone, so you see the network from the outside — the same view your visitors, clients and remote servers get. Everything runs online, needs no installation, and results appear in seconds.
What Can You Check on TCPLab?
IP address and location
Look up the geolocation, ISP and network type behind any IPv4 or IPv6 address, or check the public IP your own connection is using. Domains are resolved first, so you can paste either an address or a hostname.
DNS records
Query A, AAAA, CNAME, MX, TXT and NS records for any domain against public resolvers such as Cloudflare, Google and AliDNS, then compare the answers — the browser equivalent of dig and nslookup.
HTTP responses
Send a real GET request and inspect the HTTP status code, reason phrase, key response headers and redirect target. Only the headers are fetched, never the full page.
TCP ports
Test whether a TCP port is open on any host or IP. The probe performs a real handshake and reports open, closed or no response, so you can tell a listening service from a firewall that drops packets.
When Do You Need It?
A website will not load
Find out whether the site itself is down or just unreachable for you: check the HTTP status and headers, then compare with a probe from another region.
You need to know your egress IP
Confirm your current public IP and location, and verify that a proxy, VPN or split-tunnel rule is working the way you expect.
A port seems blocked
See whether a port is open, closed or filtered, and decide whether the problem is the service itself or a network or firewall policy.
Checking whether a site is blocked in China
If a site loads overseas but not from mainland China, it is usually blocked by the Great Firewall. TCPLab probes the same target from a mainland China node and an overseas node at the same time, then compares reachability. Domain, IP and IP + port modes are supported.