LinuxCLI

Online network diagnostic tools: dig, whois, ping, curl and more

One shared terminal for every tool below — type a command yourself, or jump to a tool's section for its syntax and an example you can run with one click.

dig — online DNS lookup tool

Query any domain's DNS records — A, AAAA, MX, TXT, NS, CNAME, SOA or PTR — straight from a real dig binary running in your browser.

dig example.com A +short

dig is the standard tool for inspecting DNS records. Point it at a domain to see how it resolves, which mail servers handle it, or which name servers are authoritative for it. You can target a specific resolver with @server, and +short trims the output to just the answer.

  • Check that a new A/AAAA record has propagated after a DNS change
  • Find the MX records to confirm where a domain's email is routed
  • Look up TXT records (SPF, DKIM, domain verification) for troubleshooting

whois — online domain lookup tool

Look up who registered a domain, when it was created, when it expires, and which registrar and name servers manage it.

whois example.com

whois queries the domain registry's public record for a given domain. It's the fastest way to check registration and expiry dates, registrar details, and delegated name servers without installing anything locally.

  • Check when a domain you're interested in was registered or will expire
  • Identify the registrar and name servers behind a domain
  • Basic due diligence before buying or trusting a domain

host — simple online DNS lookup

A lighter, more concise alternative to dig for a quick DNS resolution check.

host example.com

host resolves a domain name to its IP addresses (and vice versa) with compact, human-readable output — useful when you just want a fast yes/no on whether a name resolves, optionally against a specific DNS server.

  • Quickly confirm a hostname resolves at all
  • Sanity-check DNS from a specific resolver while debugging propagation

curl — online HTTP request tool

Send a real HTTP(S) request — GET, POST or HEAD, with custom headers — and see the response headers or body live in your browser.

curl -I https://example.com

curl is the standard tool for probing web servers and APIs. Use -I for headers only, -L to follow redirects, -H to add request headers, and -d to send a request body. Only http:// and https:// URLs are allowed, and requests run with a forced timeout and output-size limit.

  • Check response headers, status code and redirects for a URL
  • Verify a REST API endpoint responds as expected
  • Confirm security headers (HSTS, CSP, etc.) are present on a site

openssl s_client — online TLS certificate checker

Open a TLS connection to any host:port and inspect the certificate chain it presents.

openssl s_client -connect example.com:443 -servername example.com

openssl s_client establishes a real TLS handshake against a server and prints the certificate it receives — issuer, validity dates, and (with -showcerts) the full chain. -servername sets SNI, which most modern hosts require to return the right certificate.

  • Check a certificate's expiry date before it causes an outage
  • Confirm SNI is configured correctly for a multi-domain server
  • Inspect the full certificate chain for a TLS misconfiguration

mtr — online traceroute / network path tool

See the network path to a host and the latency/loss at each hop, combining traceroute and ping into one report.

mtr -r -c 5 example.com

mtr traces the route packets take to a host and repeatedly probes each hop, so you can see exactly where latency or packet loss is happening along the path. Runs here in report mode (-r) with a capped packet count.

  • Diagnose which network hop is causing latency or packet loss
  • Compare a network path over IPv4 vs IPv6

ping — online host reachability check

Send a handful of ICMP echo requests to a host and see round-trip time and packet loss.

ping -c 4 example.com

ping is the simplest way to check whether a host is reachable and how long a round trip takes. Runs here with a capped packet count, so it's a quick reachability check rather than a continuous stream.

  • Confirm a host is up and reachable from the public internet
  • Get a rough sense of latency to a server before deeper debugging

nc — online TCP port connectivity check

Check whether a single TCP port on a host is open and accepting connections.

nc -zv example.com 443

nc (netcat) here runs strictly as a one-shot connect check (-zv) against a single host:port — it reports whether the port is open, closed, or filtered. Listen mode and arbitrary data exchange are intentionally not available.

  • Verify a specific port (e.g. a database or app port) is reachable from outside
  • Quickly confirm a firewall rule change took effect