← All website monitoring tools
Nagios
20-year-old infrastructure monitoring — Core is free, XI is paid enterprise.
Free tier: Nagios Core (open source)
What it does well
- Extremely customizable through a massive library of community-contributed plugins.
- The open-source Nagios Core version is completely free to use and modify.
- Provides granular control over monitoring checks, notifications, and escalation logic.
Where it falls short
- Requires self-hosting, with no managed or SaaS option available from the provider.
- Configuration is primarily done through text files, which has a steep learning curve.
- The user interface, especially on Nagios Core, is dated compared to modern alternatives.
Alternatives to Nagios
Zabbix
freeEnterprise-grade open-source monitoring — free forever, paid support available.
Checkmk
freemiumNagios-fork modernized — popular in European DevOps, Raw is free.
Monit
freeClassic Unix process + service monitor — runs locally, restarts services if they die.
CNCF metrics + alerting standard — Blackbox exporter does HTTP/TCP/ICMP probes.