Network tools
Low-level connectivity: ICMP latency, open TCP ports and who owns an IP address.
Ping test
Send real ICMP pings to any host and read back minimum, average and maximum round-trip time plus packet loss.
Open port checker
Test whether common TCP ports — SSH, SMTP, HTTPS, MySQL and more — are reachable on a host from the public internet.
IP address lookup
Find out which network an IP address belongs to, where it is routed, its ASN and its reverse DNS name.
Other categories
Reference
Look something up without running a check.
HTTP status codes
What 301, 403, 502 and the rest actually mean, and how to fix them.
Common ports
What listens on each port and whether it should ever face the internet.
Browser errors
ERR_CONNECTION_REFUSED, NXDOMAIN, SSL errors — decoded.
DNS record types
A, MX, TXT, CNAME and friends, with real examples.