Bukkit

Commands:

/lag - Check current tick rate
/mem - Check current available memory
/lagmem or /lm - Shows server tick rate and memory usage.
/uptime - Check how long it has been since the server last restarted or reloaded
/ping [amount] and /lping [amount] - Pings google.com (or, with 1.13.1 or later, the location specified in the configuration)

Permission nodes:

lagmeter.command.lag - Gives access to the /lag command
lagmeter.command.mem - Gives access to the /mem command
lagmeter.command.lagmem - gives access to the combination /lagmem command
lagmeter.command.uptime - gives access to the combination /uptime command
lagmeter.command.ping - gives access to /ping and /lping
lagmeter.* - full access

Listed For easy copy-paste:
lagmeter.command.lag
lagmeter.command.mem
lagmeter.command.lagmem
lagmeter.command.uptime
lagmeter.command.ping
lagmeter.*