Free networking tools — no account required
Mid-troubleshoot and need a fast subnet calculation? DNS records not propagating? Certificate about to expire? These tools skip the friction — no ads, no paywalls, no sign-up.
You've got a /24 and need to split it into smaller VLANs. Or you're writing a firewall rule and need the exact broadcast address. Doing this by hand means mistakes — especially at 2am on a production network.
$ ipcalc 192.168.1.0/24 Network: 192.168.1.0 Broadcast: 192.168.1.255 HostMin: 192.168.1.1 HostMax: 192.168.1.254 Hosts/Net: 254 Mask: 255.255.255.0Open full calculator →
You changed an MX record but emails are still bouncing. A site migration finished but some users still hit the old IP. DNS propagation issues are invisible — until you look at what each resolver actually sees.
$ dig cloudflare.com MX +short 10 aspmx.l.google.com. 20 alt1.aspmx.l.google.com. 30 alt2.aspmx.l.google.com.Open DNS Lookup →
The browser says "your connection is not private" and users are calling. You need to know right now — is the cert expired? Is the chain incomplete? Is it issued to the wrong domain? This tells you in seconds, not minutes.
$ openssl s_client -connect github.com:443 2>/dev/null \ | openssl x509 -noout -subject -enddate subject=CN=github.com notAfter=Apr 15 23:59:59 2025 GMTCheck a certificate →